165 - 57 and divide that by 2. So that would be 54
90-20 leaves 70 for surfing. since surfing is 5 per hour, 70/5=14 hours she can surf.
F + 3pi = 7pi
F + 3pi - 3pi = 7pi - 3pi
Combine like terms (3pi + - 3pi = 0)
F = 7pi - 3pi
F = 4pi
The answer is 4pi
