Question

y varies directly with x. When y = 20, x = 50. Find x when y = 36.

Answer 1

since y varies directly with x, there is some constant k such that

y = k*x

Since y=20 when x=50,

20 = k*50
k = 2/5

Now you know k, and you can figure things out for other values

36 = 2/5 * x
x = 90