The 8 part is self explainatory. What I did for 21/40 is I divided [100] by 40 which gives 2.5. Then since 20/40 is .50, I find the remaining 1/40 by dividing 2.5 by [100] which gives 0.025. Now add them up and you get 0.525. You add that to 8 then you get your answer.
