Question

You went to lunch with your friend, and the bill was $19.00. Your lunch is $3.00 more than your friend's how much was your friend's lunch?

Answer 1

Robot (a.k.a [blank name]) is wrong yet again.

We'll call "your" lunch "L" and "your friend's" lunch "f"

Make 2 equations:
L + f = 19
L - f = 3

Rewrite one of the equations (in this case, the second one)
L - f = 3
L = 3 + f

Substitute L for the first equation:
L + f = 19
(3 + f) + f = 19

Solve for f:
(3 + f) + f = 19
3 + (f + f) = 19
3 + 2f = 19
2f = 16
f = 8

Your friend's lunch was 8 dollars.

***Bonus (technically not part of the problem, but just for extra practice):
Substitute f into the rewritten second equation:
L = 3 + f
L = 3 + 8
L = 11

Your lunch was 11 dollars.

Answer 2

from
L + f = 19
L - f = 3
much easier to just add them:
2L = 22
L = 11
then 11 + f = 19
f = 8

Answer 3

Your friend's lunch was $16.00.