Hello!
You can make two expressions based on what you know
x + y = 170
x - y = 110
You can add these expressions to eliminate y
2x = 280
Divide both sides by 2
x = 140
You can now put x into one of the original expression
140 + y = 170
Subtract 140 from both sides
y = 30
So the greater number is 140
Hope this helps!