Question

PLEASE EXPLAIN THIS TO ME SOMEONE!!!
The time it takes a swimmer (in hours) to go a distance of 5 miles up and down a river is given by f(x)= 4/x-1 hours and g(x)= 3/x+1 hours respectively, where x is the speed of the swimmer (in miles per hour) in still water and (2 less than or equal to x less than or equal to 20). Find the expression for the total time it takes to go 5 miles up the river and come back to the same point.
a. 7x-1/x^2-1
b. x+7/x^2-1
c. 12/x^2-1
d. 7x+1/x^2-1