How do i write 20% of n in a math format?

Show algebraically that f and g are inverse functions f(x)=x^2/-6; g(x)=square root of 2x+12

The function ƒ is defined by ƒ(x) = (x + 3)(x + 1). the graph of ƒ in the xy-plane is a parabola. which interval contains the x-coordinate of the vertex of the graph of ƒ?

Need solving this second acceleration problem.