The value of y varies directly with x. If x = 3, then y=21. What is the value of x when y=105?

x = 15

Step-by-step explanation:

given that y varies directly with x

mathematically we can express this as

y = k x, where k is a constant

step 1: find k

given x = 3 and y = 21

y = k x

21 = k (3)

k = 7

hence the equation becomes

y = 7 x

when y = 105,

105 = 7x

x = 105 / 7 = 15