Help me please with 3-111

Last Question
Because this may not be the question you want, I'll omit the first step which should be done with latex. The key to all of these except C is to invert the second fraction (turn the second fraction upside down) and multiply.
A
[tex]\dfrac{6}{5} * \dfrac{-2}{3}[/tex]
=(6*-2) / (5*3) = - 12/15 = -4/5
B
[tex]\dfrac{7}{4} *\dfrac{5}{3}[/tex]
= (7*5) / (4*3) = 35 / 12 = 2 11/12
C
Impossible to do 4/0 cannot be done.
D
[tex]\dfrac{-2}{3} /\dfrac{-5}{4}=\dfrac{-2}{3} *\dfrac{-4}{5}[/tex]
= (-2*-4)/(3*5) =
8/15