Question

I need help with this problem

Answer 1

`(3*4)+(6*a)=30`

`6a=18 \\ a=3`
OR

`(-2*4)+(5*a)=7`

`5a=15 \\ a=3`

Answer 2

`\left[\begin{array}{ccc}3&6\\-2&5\end{array}\right] \cdot \left[\begin{array}{ccc}4\\a\end{array}\right] = \left[\begin{array}{ccc}30\\7\end{array}\right] \\ \left[\begin{array}{ccc}3\cdot4+6\cdot a\\-2\cdot4+5\cdot a\end{array}\right] = \left[\begin{array}{ccc}30\\7\end{array}\right] \\ \left[\begin{array}{ccc}12+6a\\-8+5a\end{array}\right] = \left[\begin{array}{ccc}30\\7\end{array}\right] \\\\ 12+6a=30\\ -8+5a=7\\\\ 6a=18\\ 5a=15\\\\ a=3\\ a=3\\\\ \boxed{a=3}`

I'm not good at this stuff. There may a quicker and better way to solve it.