[tex]\displaystyle\\a)~~~3\cdot\left(\frac{2}{3}\right)-4\cdot\left(-\frac{7}{4}\right)=\frac{3\cdot2}{3}+\frac{4\cdot7}{4}=2+7=9~~~\text{(Correct)}\\\\\\b)~~~3\cdot\left(-5\right)-4\cdot\left(-6\right)=-15+24=9~~~\text{(Correct)}\\\\\\c)~~~3\cdot\left(1\right)-4\cdot\left(-\frac{3}{2}\right)=3+\frac{4\cdot3}{2}=3+2\cdot3=3+6=9~~~\text{(Correct)}\\\\\\d)~~~3\cdot\left(-1\right)-4\cdot\left(3\right)=3-12=-9~~~\text{(Wrong)}[/tex]
