system of equations word problem

Mr. Day and Ms. Knight gave the same test consisting of 20 short-answer questions, but marked their test papers using different grading systems. Mr. Day awarded 5 points for each correct answer, made no deduction for an incorrect or omitted answer, and then added 10 points to the total. Ms. Knight gave 6 points for each correct answer and subtracted 1.5 points for each incorrect or omitted answer. Two students in different classes answered the same number of questions correctly and received the same test grade. Determine, using algabraic method, the test grade both students received. Confirm your answer graphically or by constructing a table using your graphing calculator.