Answer:
y = 2x
Step-by-step explanation:
Given y is directly proportional to x then the equation relating them is
y = kx ← k is the constant of proportion
To find k use the condition when x = 4, y = 8, that is
8 = 4k ( divide both sides by 4 )
2 = k, thus
y = 2x ← equation of proportion
