What two numbers are 7 units from 0 on a number line?
a. 3 and -4
b. 7 and 8
c. 7 and -7
d. 9 and 2

O                                      *                                       o

l     l     l     l     l     l     l     l     l     l     l     l     l     l     l
-7  -6  -5  -4  -3  -2  -1    0    1    2    3    4    5   6    7

As you can see on the number line, both -7 and 7 are each 7 units away from 0.