Explanation:
in such cases we can simply add both equations, which eliminates one variable. then we since the result for the remaining variable.
with that we go into one of the original equations and solve for the second variable.
A + B = -3
A - B = 5
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2A + 0 = 2
2A = 2
A = 1
using e.g. the first original equation :
1 + B = -3
B = -4