Rosa works in an office building with many floors. from her office, she goes down 2 floors for a meeting. then, she goes up 7 floors to have lunch. after lunch, she goes down 15 floors to the first floor. what floor is rosa's office on?

Since Rosa ends up on the first floor, we'll set the equation equal to 1. We don't know Rosa's floor, so we'll set her floor as the unknown x. When she goes down, we'll subtract from her floor (x) and when she goes up, we'll add.

x= Rosa's floor
down 2= subtract 2
up 7= add 7
down 15= subtract 15
ends up on 1 so equation equals 1

x - 2 + 7 - 15= 1
combine like terms
x - 10= 1
add 10 to both sides
x= 11

ANSWER:
Rosa works on the 11th floor

Hope this helps! :)