A 100-gallon fish tank fills at a rate of x gallons per minute. The function is F(x)=100/x. if the tank has been filling for 20 minutes, the total time to fill the tank is represented by the function f(x)=100/x+20. Which graph represents this

The second graph is correct.

There will be a vertical asymptote at x=0, since we cannot divide by 0.  Using the x-axis on the second graph, if we substitute 5 in for x, we have 100/5+20 = 20+20=40.  There is a point on this graph here.  Using 10 for x, we have 100/10+20 = 10+20 = 30.  There is a point on the graph here.  Every point matches.