Question 271023
we start with these equations
(1) {{{B+A=29}}}
(2) {{{B-A=5}}}
step 1 - add down to get
(3) {{{2B = 34}}}
step 2 - divide to get
(4) {{{b + 17}}}
step 3 - by substitution, 
{{{A = 12}}}