Answer
Equation: y=3x
y=30 when x=10
Work Step by Step
Since we know that y-varies directly with x, we can plug in the values for y and x and solve for k
9=k(3) (Divide both sides by 3)
3=k
So plug k in for the general form of a direct variation (y=kx):
y=3x
Now in order to find the value of y when x=10, plug this value of x into the equation above:
y=3(10)
y=30
