Jesse E. answered 04/26/19
Experienced tutor for TEAS, chemistry, and biology
You would use a system of equations:
X + Y = 18
20X + 15Y = 330
X = 18-Y
20(18-Y) + 15Y = 330
360 (- 20Y +15Y) = 330 Combine Like Terms
360 - 5Y = 330 Substract both sides by 360
-5Y = -30 Solve for Y
Y = 6
X + 6 = 18
X = 12