A student claps once when standing 100 m away from a large wall. The speed of sound in air is 330 m/s. How long after clapping does the student hear an echo?

c

explanation:

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.

i think the answer is tomato juice? not entirely sure though