You have 3 and 1.

You have 7 and 1.

-Take one number from the top and one number from the bottom.

-Pair them together and multiply them.

-There will be 2 numbers left unselected.

-Pair them together and multiply them.

-See if you can add them or subtract them to obtain 4

-If you can, place each paired number in an opposite bracket. You know which values are "stuck" to a so then you just need to work out the signs.