Find all quadruplets of real numbers (a,b,c,d) that satisfy
a + b = 11
b + c = 10
c + d = 13
d + a = 14
So we add 11+10+13+14 to get 48 which is 2 of a+b+c+d so we divide by 2 to get a+b+c+d=24 and to get the variables a=14-d
b=-3+d
c=13-d
so we find that (a,b,c,d)=(7,4,6,7)
