need a nested if/and formula for a single cell sorted out - semi complex but beyond me

[Omegaman2]

The spreadsheet must remain on one sheet. Cells, f3,f4,f5,and f6 are all for input purposes. The formula in cell f 8 is currently =(((F3/12)*2)*F6)+(((F4*60)+F5)*0.84)-30 and works perfectly in most cases. However, I need it to modify it's behavior under certain cases. Case 1: If f3=15 or less AND f5=22 or less, then f8 should display "FREE". Case2= Any time that f8 would return 0 or less (a negative number), f8 should display "FREE". No other cells are available for calculations, so all trickery must be preformed within cell f8.