Please help.

This is a little equation that you are being asked to rearrange.

$$ax=b\\$$

You want the x out the front by itself.   SO you have to get rid of the   $$a$$

You can do this by dividing the LHS by  $$a$$    but the equation must stay balanced.

Whatever you do to one side you must also do to the other side.

so this is what happens

$$\\ax=b\\\\ \dfrac{\not{a} x}{\not{a}}=\dfrac{b}{a}\\\\ x=\dfrac{b}{a}\\\\$$

Thanks! 

What is the LHS?

It means Left Hand Side   LHS

Ok thank you.