Chapter 9 - 9.2 - Two-Variable Linear Systes - 9.2 Exercises - Page 648: 54a

$a=-44.21$

Multiply the first equation by $3.7$ and multiply the second equation by $-3$. Therefore, the system of two equations is: $11.1 b+13.69 a=388.50 \\ -11.1b-14.07a=-371.70$ Add both the equations. This yields $-0.38 a=16.80 \implies a=-44.21$ Thus, $a=-44.21$