Posted by Beth on .
Suppose that y is directly proportional to x.
If y = 10 when x = −5, what is the value of y when x = 30?

maths 
Reiny,
"y is directly proportional to x"  y = kx , where k is a constant
for the given:
10 = 5k
k = 2
so y = 2x is your equation:
so when x = 20 , y = ......