What is the solution for
a=(2x+5)(x+3)

Alright, to simplify the question given, we need to FOIL (2x+5)*(x+3). We can do this two different ways.

The first way is to multiply the first term of both, the outer terms of both, the inner terms of both, then the last terms of both and then add those all up (picture 1). Remember to simplify any numbers with the same variable!

The second way is to set up a box with the first set of parenthesis on the top and the second pair of parenthesis on the side (picture 2) and then multiply where all the boxes cross, and then add up what you get in the end (picture 3). Remember to simplify any numbers with the same variable too!

No matter which method you choose, you should end up with 2x^2+11x+15=A as your final answer.

A square has equal sides. To find the area, you multiply the length and the height.
x*x=121
x^2=121
x=11
The length of each side is 11

A square has equal sides. To find the perimeter, you add all the sides together.
x+x+x+x=28
4x=28
x=7
The length of each side is 7