So A+A = 16 meaning that A is 8 and B+A=24,to find the answer you have to subtract 8 from 24 which is 16 and finally C+B=40,since we know that B is 16 we just subtract it from 40 and the answer is 24 now comes the last question C+A-B which is 24+8-16 now we have to add before we subtract,24 +8 = 32-16= 16. Did I get it right?