You and a friend spent a total of $15 for lunch. Your friend’s lunch cost $3 more than yours did. How much did you spend for lunch?

your total spent is $15

Your friend spent $3 more than you, this is represented by 3+x.

You spent an unknown amount of money, this is represented by x.

So, your equation is 15=3+x+x.

This becomes 15=3+2x.

You then subtract 3 to the other side to get.

12=2x

Then divide 12 by 2, in order to leave variable "x" by itself.

6=x is the amount you spent on lunch.

Your friend spent $3 more so add $3 to the amount you spent to get...

$9 spent by your friend.

You=$6

Friend=$9

Total=$15

1/800 is the right answer