Suppose y varies directly as x and y=27 when x=3. Find x when y = 45.

'Varies directly' most likely means an equation of the form y = x + k

Where k is a constant. So as x increases by some amount, y increases by that same amount.

change in y = change in x

y2 - y1 = x2 - x1

45 - 27 = x2 - 3

18 = x2 - 3

21 = x2

when y = 45,x = 21