Write 7\8 as a decimal and as a percent

1) 0.5^3+0.3^3=
0.5^3=0.125
0.3^3=0.027
0.125+0.027=0.152

2)Let X be the number:
X*7=6*50
7X=300
X=42.857

3) If it takes 3 identical pumps to fill a pool, one pump will take 8*3=24 hours to fill the pool. If you have 4 pumps, it will quadrupal the speed, making it take 24/4=6 hours.

Hope I helped!