Answer: b= 4a
( This is the correct answer, which is supposed to be option b, but a negative sign was put instead of an equal sign, so you can change appropriately)
Explanation:
Given that a and b vary directly, can be expressed as
a ∝ b
Introducing the constant of proportionality, k, we have that
a = kb
so when a= 2, b= 8 and the constant becomes
2 = k8
k = 2/8=1/ 4
a= 1/4b
Such that
b=4a