Melanie has a $60 so far to buy a lawn mower. this is 20% of the price of the lawn mower. what is the full price of the lawn mowers that she wants to buy?

--Percent means out of 100, so 20% = 20/100

The prob in other words is asking
  --  $60 is 20% of what number?

'$60'   --          --->  60
'is'       --          --->  =
20%    --         ---> 20/100
'of'     --            ---> * (multiply)
'what number'  ---> x  (variable)

Suppose that Judy completes exercises on Monday. Since she doubles the amount of exercises every day, she will complete exercises on Tuesday, exercises on Wednesday, exercises on Thrursday and exercises on Friday.

So, she completed exercises.

She still has 7 problems left, which means that she did problems so far.

So, we have

Here's the number of exercises per day: