Question

The cost, c, of a ham sandwich at a deli varies directly with the number of sandwiches, n. If c = $54 when n is 9, what is the cost of the sandwiches when n is 3?

Answer 1

if c varies directly with n, then

c = kn
plug in c = $54 and n = 9 to solve for k
then re-write c = kn, using that k value

finally, plug in n = 3 into the new equation and solve for c