You can divide the whole expression by -3:

Recalling that

Let's compare the middle term:

So, we want to complete

Which differs from
by 16. So, if we add 16 to both sides, we have

Answer:
1/5 divided by 4 equals to 0.05
Answer:
There must he a circulation. May not be causation.
If 1/6 of the pan was left and there were 2 pieces left you just need to set 1/6 equal to 2/some number, this allows you to say that 1/6=2/x --> x/6=2-->x=12.
My explanation might be a little poor since this becomes fairly fundamental later on but hopefully it helps.