You are going to take a test that includes both calculator problems and non-calculator problems. You can do a calculator problem in 2 minutes and a non-calculator problem in 4 minutes. You have 40 minutes to take the test and may answer no more than 12 problems. Letting c = the number of calculator problems attempted and n = the number of non-calculator problems you attempted, find the equation that you would use to consider the number of minutes each problem takes.