The first step is to understand what it means when a number has an exponent. The “power” of a number indicates how many times the base would be multiplied by itself to reach the correct value.
The second step is to write the number in the base-exponent form, and lastly calculate what the final result would be. Consider the example of 2 to the power of 4: in exponent form that would be
So re-applying these steps to our particular problem, we first convert our word problem to a base-exponent form of:
To simplify this, all that is needed is to multiply it out:
21 x 21 x 21 x 21 x ... (for a total of 90 times) = 99939351280438708031445518371998420381925640460777151271993282802216310828347110292943440178518117655180955116549443801
Therefore, 21 to the power of 90 is 99939351280438708031445518371998420381925640460777151271993282802216310828347110292943440178518117655180955116549443801.