You should use your calculator for such simple sums. It is far quicker and involves fewer key depressions. I could tell you that the answer is 207 but how can you be sure that I did not make a mistake? Or that I am not messing about?
-43 + 21 = -22
43
B=26 you just have to isolate the variable, so subtract 17 from 43 because the rule in algebra is that whatever you do to one side, you have to do to the other
89 plus 43 plus 37 equals 169.
19 + 43 + 13 = 75
25
16 plus 27 equals 43.
43
43
-17
60
77