a. 3
Solution:
from the question, we can get the following formula:
[tex] \: \: \: \: \: \:\: \: \: \sf4 \frac{1}{2} \times \frac{2}{3} \\ [/tex]
[tex]\: \: \: \: \: \: \: \sf = \frac{9}{2} \times \frac{2}{3} \\ [/tex]
[tex]\: \: \: \: \: \: \: \sf = 3[/tex]
So he used 3
Hope it helps
