>>12183403It's a system of 4 equations with 4 variables. We name them in the following way:
a + b = 8
+ +
c - d = 6
= =
13 8
So we can rewrite the equations to make them more clear:
a + b = 8 (1)
c - d = 6 (2)
a + c = 13 (3)
b + d = 8 (4)
There are many ways to solve this (assuming it has a solution), the simpler is to add (2),(4) and subtract them from (3). Then you would get
a - b = -1 (5), which with (1) forms a system with two variables and two equations. It can be solved in many ways aswell but if you add (1) and (5) you get
2a = 7 or that a = 7/2. Then from that using any equation of the system (1) or (5) you can get b, which is 9/2. To finish you can either do a similar trick for c and d (try it if you want) or you can simply notice that from equation (3) you can get that c = 13 - a = 13 - 7/2 = 19/2 and from equation (4) d = 8 - b = 8 - 9/2 = 7/2
