Hi all, really need some help with this!

I know it's super duper easy but I won't get this without a proper explenation, please help me

Okay so we are supposed to simplify this;

4a/5 * 15/2a

I think I know how to do it in theory but I just can't seem to get the right answer. Im thinking of inverting the first one and then multiplying the second one by 2 in order to get the same nominator, but it's still not right.

Just for the heck of it i'd like some help with this one aswell. It's the same thing - Simplify

2/9z * 3z^2/10