Anais, a math teacher, noticed that the average grade on an exam, GGG, given that nnn students watch the related video can be given by the function G(n)=50+1.5nG(n)=50+1.5nG, left parenthesis, n, right parenthesis, equals, 50, plus, 1, point, 5, n. She also noticed that the number of students, SSS, who watch an mmm minute video can be modeled by the function S(m)=30-mS(m)=30−mS, left parenthesis, m, right parenthesis, equals, 30, minus, m. Find an explicit expression that gives the average grade on an exam if the related video is mmm minutes.