There are different formulas for each different shape.
D the forth one bottom right side
$2.50(f) + $4(n) = Total Cost
$2.50(9) + $4(9) = Total Cost
$22.50 + $36 = Total Cost
$58.50 = Total Cost
The full length of one line times the length of the line outside the circle is equal the the other line.
(7+x)*7 = (13 +8) * 8
Simplify:
7x +49 = 21 * 8
7x +49 = 168
Subtract 49 from each side:
7x = 119
Divide both sides by 7:
x = 17
The answer is B. 17
