suppose a square has a side length by the expression x+5/8x. what is the perimeter of the square?

This is equal to (x -5)(x - 5), or (x - 5)². 
Therefore, using the formula given above, the side's length is equal to (x - 5). 

Muliply that by four to obtain the perimeter. 

4(x - 5) = 4x -20. 

For the second problem, disregard the brackets since there are no other operations besides subtraction and addition. 

So it would become 3x^4 -x + 2 + 9x^5 - x² + x. 

Now simplify everything and rewrite it in decreasing terms of power, 

9x^5 + 3x^4 - x² + 2.