1.If y varies directly with x
Introduce the constant term k
2.y=kx
where k is the constant term
substitute the value of x and y to form the law
-1=3k
k=-1\3
:y=-1\3x....is the law
To find the value of y when x is 9
Reinstate the law which is y=-1\3x and substitute the value of x to find y
y=-1\3*9
y=-3