we have to divide 9/10 by 3/12.
if we divide by a fraction, we can instead multiply by it's inverse:
[tex] \frac{9}{12}/ \frac{3}{12} = \frac{9}{12} * \frac{12}{3} [/tex]
so now we count:
[tex] \frac{9}{12} * \frac{12}{3} =\frac{9}{1} * \frac{1}{3}=3 [/tex]
so we can cut exactly 3 pieces!