Two different totals anchor these rates: 1,000 orders received and 5,000 lines shipped. One rate counts whole orders against the order total, the other counts individual lines against the line total, so the task is keeping each count over its own base and never mixing the two totals.
The on-full rate is the number of orders delivered complete as a percentage of the orders received. There were 850 complete deliveries out of 1,000 orders, so the on-full rate is 850 / 1,000 = 85 percent. That fills the on-full selection.
The short-ship rate is the number of short-shipped lines as a percentage of the lines shipped, not the orders received. The denominator is the 5,000 lines, and 500 were short-shipped, so the short-ship rate is 500 / 5,000 = 10 percent. That fills the short-ship selection.
The trap the question is built around is using the order total of 1,000 as the base for the short-ship rate, because orders feel like the natural unit of a shipment. A reader who takes the short-shipped lines over orders gets 500 / 1,000 = 50 percent and reports that as the short-ship rate. But the short-ship rate counts lines against lines, so the 5,000 is its base, not the 1,000. That is where 50 percent comes from.
Every remaining option is a specific named misread, not filler. 15 percent is the order-level shortfall: the 150 orders not delivered complete (1,000 − 850 = 150) over the 1,000 orders, 150 / 1,000 = 15 percent, the complement of the on-full rate reported in the on-full slot instead of the rate itself. 90 percent is the line-complete rate: the lines that were NOT short-shipped, 5,000 − 500 = 4,500, over the 5,000 lines, 4,500 / 5,000 = 90 percent, the complement of the short-ship rate, correct arithmetic on the right base but answering the opposite question for the short-ship slot. 70 percent is the double-penalized on-full count: a reader subtracts the 150 incomplete orders a second time from the 850 complete orders, 850 − 150 = 700, then divides by the 1,000 orders, 700 / 1,000 = 70 percent, charging the shortfall against the complete count it was already removed from.
The discipline: a named rate carries a fixed base, and the unit of the numerator has to match the unit of the base. The on-full rate is orders over orders; the short-ship rate is lines over lines. Mixing the two totals, or reporting a complement, or double-counting the shortfall is the slip.
On-full rate: 85 percent. Short-ship rate: 10 percent.