Answer:
[tex]\large\boxed{a=-\dfrac{1}{10}=0.1}[/tex]
Step-by-step explanation:
[tex]\left\{\begin{array}{ccc}3=10a+b\\2=20a+b&\text{change the signs}\end{array}\right\\\\\underline{+\left\{\begin{array}{ccc}3=10a+b\\-2=-20a-b\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad1=-10a\qquad\text{divide both sides by (-10)}\\.\qquad-\dfrac{1}{10}=a\Rightarrow a=-\dfrac{1}{10}[/tex]
