Block $A,$ with mass $m_A=10kg,$ is pulled to the right a distance $x=0\mathrm{.}4m$ from the position it would have if the spring were relaxed $)=(0.$ It is then released from rest. Assume ideal string, pulleys and wheels. The spring has constant $k=90\frac{N}{m}.$

A$.$ What is the acceleration of block A just after it is released?

The Answer is $($A$)=(-32\mathrm{.}4$ m$/$s$^2)$

I need help with the steps to understand how they got the answer.