im assuming that astroman read the question another way, but I'm reading it as 4^a + (3x4^a) = 8
so first factorise LHS
4^a (1 + 3) = 8
4^a (4) = 8
divide both sides by 4
4^a = 2
LHS 4^a is also equal to 2^2a, so
2^2a = 2
from direct comparison
2a = 1
a = 1/2 hope that helps