First factor the each term in the expression.

40a =  2 · 2 · 2 · 5 · a

8 =  2 · 2 · 2

The GCF is the product of the common prime factors in each term.

GCF = 2 · 2 · 2 = 8

Write each term as a product of the GCF and its remaining factors.

8 + 40a = 8(1) + 8(5a)

Combine like terms uisng distribuitve property: ab + ac = a(b + c).

8 + 40a = 8(1 + 5a)

Simplified expression is 8(1 + 5a) .