The system of equations:

The system of equations:
S + W = To the
we Express all variables using B:
E = 124 + B
W = 70 + B
To = 587 - L = 587 - (W + 215) = 587 - (B + 70 + 215) = 302 - B
Substitute in the equation:
124 + B + A 70 + B = 302 - B
solve it
B + b + B = 302 - 124 -70
3*B = 108
B = 36
Knowing the value of B determines the remaining unknown without any problems.