This looks like a classic PEMDAS exercise.
PEMDAS is the memory word to help you remember the ORDER in which to do different operations, when several different operations have to be done. It means . . .
Parentheses
Exponents
Multiplication
Division
Addition
Subtraction .
So we have to simplify 5³ + (10 - 5) - 40 .
Lets go through PEMDAS one step at a time and do the operation as we come to each letter.
Parentheses
The quantity in parentheses is (10 - 5). That's 5 .
Now the expression is 5³ + 5 - 40 .
Exponents
The term with an exponent is 5³. That's (5 · 5 · 5) = 125 .
Now the expression is 125 + 5 - 40 .
Multiplication
There isn't any multiplication needed in our expression.
Division
There isn't any division needed in our expression.
Addition
The addition in our expression is 125 + 5 . That's 130 .
Now the expression is 130 - 40 .
Subtraction .
The subtraction in our expression is 130 - 40. That's 90 .
And there we are.
After it's been simplified, the whole expression is 90 .