Can someone answer. there is one problem. you!

If f(x)=x^3 and g(x)=2x+7 when g(x)=-5

Gabrielle's age is three times mikhail's age. the sum of their ages is 40 . what is mikhail's age? __ years old

Megan and desmond each add the same amount of water to their aquarium megan makes 5 ml of chemical solution with every gallon of water for her aquarium desmond mixed 8 ml of chemical solution for every 2 gallon of the water for his aquarium.