Writing a direct variation equation? Help

Suppose y varies directly as x. Write a direct variation equation that relates x and y. Then solve. Please explain and show work :)

If y = 6 when x = 10, find x when y = 18

If y = 4 1/4 when x = 3/4, then find y when x = 4 1/2

1) y = kx
so k = y/x = 6/10 = .6
so y = .6x
when y = 18
18 = .6x
x= 18/.6 = 180 /6 = 30

2) Follow the method above.