Given a series of equation , calculate the result of all the variables

{"x1 = x2 + x3", "x2 = x4 + x3", "x3 = 5", "x4 = 1"}

calculate result of all variables i.e
x1 = 11
x2 = 6
x3 = 5
x4 = 1

i started with recusrsion but couldnt complete it. Any thoughts?