The base of an exponent is a number that is raised to a certain power.
In 152, 15 is the base and 2 is the exponent. You can read 152 as 15 raised to the power of 2.
To get an answer for 152, you can just multiply 15 by itself.
152 = 15 × 15
Other examples
In 46 , 4 is the base
In 13 , 1 is the base
In (-9)6 , -9 is the base
In -96 , -9 is not the base. 9 is the base