Since (2, -3) is a solution, that means x = 2 and y = -3 would satisfy the equations.
x + by = 5 Ax - 3y = -1
2 + b*-3 = 5 A*2 - 3*-3 = -1
2 - 3b =5 2A + 9 = -1
-3b = 5 - 2 2A = -1 - 9
-3b = 3 2A = -10
b = 3/-3 A = -10/2
b = -1 A = -5
b = -1 and A = -5
Hope this helps.