a + 3b =13 ............... (1)
a + b = 5.............. (2)
By substitution from equation (1) a = 13 - 3b
Substituting for a in equation (2) yields
13-3b+b = 5
13-2b = 5
Bringing like terms together
13-5 = 2b
2b = 8
2b/2 = 8/2
b = 4
From Equation (2) a + b=5
a + 4 = 5
a = 5 -4
a = 1