How am i able to solve problems like this? like is something i can just plug numbers into?

so for this type of problem you would want to use the Pythagorean theorem. its a squared plus b squared equals c squared. you use this because it makes a triangle. c is your hypotenuse which is the longest side of the triangle. so you plug in what you can and solve to find the missing variable. in this case, the base equals the square root of 80 or approximately 8.94

to find the perimeter of the rectangle this is the expression:

x-9+x-9+3x-4+3x-4=138

if we simplify it:

8x-26=138

remember, 138 is what it all adds up to

the length is 11.5cm

the width is 57.5cm

the area is 661.25cm^2

the answers might not be correct use at own risk