If f(x) =2x and g(x)= x squared -1, which statement is true?

a. (f*g) (x)=2x squared -1
b. (f*g) (x)=2x(x squared -1)
c. (g*f) (x)= 4x -1
d. (g*f) (x)= 4x squared -1

Hi my sisters and brothers can tell me the answer because i don’t understand the question

Jackie purchased 3 bottles of water and 2 cups of coffee for the family for $7.35. ryan bought 4 bottles of water and 1 cup of coffee for his family for 7.15. how much does each bottle of water cost? how much does each cup of coffee cost?

What is the missing step in this proof ?