ok
Hose 1 = H = 5g/2 m
Hose 2 = M = 10g/8 m = 5g/4m
Hose 1 + Hose 2 = Total
5g/2 m + 5g/4 m = Total
10g/4m + 5g/4m = Total
15 gallons/4 min = total
15 gallons ---------------------------- 4 min
750 gallons -------------------------- x
x = (750 x 4) / 15
x = 3000 / 15
x = 200 min
Result. It will take 200 min to fill the pool