12 should be 25% just divide 10 by 40 which gives you .25 then multiply by 100 and that gives you 25%
20 should be 33.33& divide 7 by 21 that gives you .3333 muliply by 100 that gives you 33.33%
21 should be 7.5 since you multiply the percent by the whole to get the part which would be .15 multiply by 50 which is 7.5