4^x is equal to 2^(2x), so the equation can be written as 2^(2x)+2^(1+2x) = 50. Factoring out 2^(2x), one gets 2^(2x)(1+2)=2^(2x)(3)=50, which is equivalent to 2^(2x)=50/3. Taking the logarithm base 2 of both sides gives 2x = log (50/3) or, equivalently, x = 1/2 log (50/3), where the logarithm is base 2.