x+y=10----(1)
x*3+y*3=100----(2)
From(1)
y=10-x------(3)
Sub(3)into(2):
x*3+(10-x)*3=100
x*3+(10-x)(10-x)*2=100
x*3+(10-x)(x*2-20x+100)=100
x*3+10x*2-200x+1000-x*3+20x*2-100x=100
30x*2-300x+1000=100
30x*2-300x+900=0
x*2-10x+30=0
x*2=10x-30
y*2=10y-30
x*2+y*2=10x-30+10y-30
x*2+y*2=10x+10y-60
x*2+y*2=10(x+y-6)-----(4)
Sub (1) into (4)
x*2+y*2=10(10-6)
x*2+y*2=40