Each sentence is divided into four parts, in which one has error in it. Choose the incorrect part as your answer choice. If all the parts are grammatically correct, choose “No Error” as your answer choice.

After failing the first (A)/ run at 30 seconds, the cadet (B)/ had to schedule a repeat tryout so (C)/ that he could meet the goal (D).

Correct option is B

The error is in part (B). Here, ‘at’ must be replaced with ‘by’. We use by to talk about measurements, and increases and decreases in amounts:
Ex- My bedroom is just three metres by two metres!