Answer:
x = 30
Explanation:
The perimeter is the sum of all of the sides of a shape. Therefore, because the sum is equivalent to 104 inches and we are given the lengths of all three sides, we can add the three sides together and set them equal to 104 in order to solve for x.
(x + 3) + (x + 4) + (x + 7) = 104 Drop the parentheses.
x + 3 + x + 4 + x + 7 = 104 Combine like terms (variables first!).
3x + 3 + 4 + 7 = 104 Now, combine constant terms.
3x + 14 = 104 Subtract 14 from both sides.
3x = 90 Divide by 3 on both sides of the equation.
x = 30