The base of the log on the left hand side is 2. Recall the rule of logarithm,
loga b = k
Given that a is the base, it can be written as
b = a^k
By applying this rule on the given equation, we have
x + 3 = 2^4
x + 3 = 16
x = 16 - 3
x = 13
3.7m questions
4.8m answers