h= Hamburger
f= fries
3 h + 4f = 1580 calories - equation 1
If each order of hambruger is 60 cal more than fries then we turn it into...
h - f = 60 calories - equation 2
And flip over the equation to make h the subject, it is possible to do it for f but ny preference is h.
h = 60 + f - equation 3
3 ( 60 + f ) + 4 f = 1580 cal
180 + 7f = 1580 cal
7f = 1580 - 180 cal
7f = 1400 cal
f = 1400 / 7
f = 200
So each order of fries have 200 Calories
We take equation 1 and substitute it into the equation.
3h + 4 (200) = 1580 cal
3h + 800 = 1580 cal
3h = 1580 - 800 cal
3h = 780
h= 260
Each order of a hambruger has 260 calories to check the answer we substitute again.
3( 260) + 4(200) = 1580
780 + 800 = 1580
Answer is correct