Answer
5 to the power of 7
Explanation
Multiply the length by the width. When multiplying numbers with exponents and similar bases, you can just add the exponents. If this doesn't make sense I'll show you.
The length is 5*5*5*5.
The width is 5*5*5.
Multiply this, and you get 5*5*5*5*5*5*5.
This is 5 times itself seven times.
The area of the rectangle is 5 to the power of 7.
