This can be a nasty problem to find the right combination of numbers to work out right! However, notice that the first and last are both perfect squares!! (I just LOVE perfect squares, don't you know!!) Try that combination first. It doesn't always work, but it's the best place to start!!
First times first looks like this, with 4y*4y:
(4y ____)((4y____)
Last times last would be 9*9:
(4y___9)(4y___9).
What signs will make this middle term come out to -72? Try both making both signs negative.
