GRE Sample Test 5 Quantitative Reasoning 2

To isolate a, divide both sides of the equation by 16 to arrive at:
a =

64b

16

Next, express the bases in base-2. 64 = 26, so the numerator = (26)b = 26b. Expressed in base-2, the denominator = 24. So the equation simplifies to:
a =

(26b)

24

Since we’re dividing terms with the same base, we’ll keep the base and subtract the exponents to arrive at: 2(6b−4).