Please help and explain!

For one history test, keith had to answer 40 questions. of these 40 questions, keith answered 28 of them correctly. what percent did keith get on his history test? round your answer to the nearest tenth if necessary

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=