Question 56613
X+Y=80
X=80-Y
850*X+1,050Y=78,200
NOW SUBSTITUTE 
850(80-Y)+1,050Y=78,200
68,000-850Y+1,050Y=78,200
200Y=78,200-68,000
200Y=10,200
Y=10,200/200
Y=51
X+51=80
X=80-51
X=29