Which equation represents the number of points in the problem below?

A test is worth 50 points. Multiple-choice questions are worth 1 point, and short-answer questions are worth 3 points. If the test has 20 questions, how many multiple-choice questions are there?

A. m+3s=20
B. m+3s=50
C. m+3s+20=50
D. m+s=50

Monica build a remote control toy airplane for science project to test the plane she launched it from the top of a building the plane travel a horizontal distance of 50 feet before landing on the ground a quadratic function which models the height of the plane in feet relative to the ground at a horizontal distance of x feet from the building is shown