If $3\mathrm{x}-4\mathrm{y}+5=0$ and $\mathrm{ax}+2\mathrm{y}+4=0$ are parallel to each other then a=

Two lines ${\mathrm{a}}_1\mathrm{x}+{\mathrm{b}}_1\mathrm{y}+{\mathrm{c}}_1=0$  and ${\mathrm{a}}_2\mathrm{x}+{\mathrm{b}}_2\mathrm{y}+{\mathrm{c}}_2=0$ are parallel if and only if  $\frac{{\mathrm{a}}_1}{{\mathrm{a}}_2}=\frac{{\mathrm{b}}_1}{{\mathrm{b}}_2}$
It implies that   $\frac{3}{a}=\frac{-4}{2}$
Cross multiply and then simplify 
 $\begin{array}{c}-4a=6\\ a=-\frac{3}{2}\end{array}$ 
Therefore, the value of a is   $a=\boxed{-1.5}$