Answer
a) 5
b) 5.5
Work Step by Step
To use the ruler, we subtract the smaller measurement at one end of the ruler from the larger measurement at the other end of the ruler. Doing this, we find:
Case A:
$$ AB=5-0 \\ AB=5 $$
Case B:
$$ CD= 7 -1.5 \\ CD = 5.5$$
