Multiplying ,you get 18x^2+21x-24x-28. You simplify to get:
18x^2-3x-28.
There are 10 sides becuase the equation set up is
and equal it to 144.
Solve for n and get 10
Line 3
since he added which is against the order of opreation rule he was supposed to multiply first then add
again what he was supposed to do is
Line 2:21+5+6(2)
Line 3:21+5+12
Answer:

Step-by-step explanation:
We are given an expression and we have to transform it into an expression with exponent.
5th root of x can be written as 
![(\sqrt[5]{x^7})^3\\\\((x^7)^\frac{1}{5} )^3](https://tex.z-dn.net/?f=%28%5Csqrt%5B5%5D%7Bx%5E7%7D%29%5E3%5C%5C%5C%5C%28%28x%5E7%29%5E%5Cfrac%7B1%7D%7B5%7D%20%29%5E3)
The powers outside will be multiplied as: 

where the exponent is
and it is a rational number by definition of rational numbers