WebWork = 28%

Four exams = 6% each
A final = 28%
Labwork = 20%

Suppose you obtain 100 percent credit on all WeBWorK assignments for this class. What is the minimum average percentage on the exams and labwork that will still get you an A in this class? (Remember an A is greater than or equal to a 90%)

Your answer should be a number between 0 and 100. You may enter a fraction instead of a decimal.

I have no idea how to set up this problem. Please help!