answer : -90 = -100+x → x = 10
explanation : to solve for x, you are simplifying both sides of the equation, then isolating the variable.
step 1 : move the variable to the left-hand side and change its sign.
ex : -90-x = -100
step 2 : move the constant to the right-hand side and change its sign.
ex : -x = -100+90
step 3 : calculate the sum
ex : -x = -10
step 4 : change the signs on both sides of the equation
ex : x = 10
solution : x=10
hope this helps !
- audrey ♡
