Answer:
The difference is 48 meters
Explanation:
The question is
What is the difference of the hikers' altitudes?
Let
x -----> the Melissa's altitude in meters
y ----> Brian's altitude in meters
we have that
---> is positive because is above sea level
---> is negative because is below sea level
Remember that the sea level is the altitude equal to zero
Find the difference
To find out the difference of the hikers' altitudes, subtract Brian's altitude from Melissa's altitude
so
![27-(-21)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/du5i3q4q9cekwkd0yzdhnbyfiupvckepie.png)
Remember that (-1)(-1)=+1
![27+21=48\ m](https://img.qammunity.org/2020/formulas/mathematics/middle-school/m0hx0idshwvzxh4yg8w6j9sl95m83ajtr0.png)