Write 2 equations:
Monday: 5A + 2B = 6 hours
Tuesday: 3A + 8B = 7 hours
Multiply Monday by -4:
Monday: -20A -8B = -24
Now add Monday and Tuesday together:
-17A = -17 hours
Divide both sides by -17
A = -17/ -17 = 1
Plan A is 1 hour long.
Now replace A in Monday with 1 and solve for B:
5(1) + 2B = 6
5 + 2B = 6
Subtract 5 from both sides:
2B = 1
Divide both sides by 2:
B = 1/2
Plan A is 1 hour, Plan B is 1/2 hour.