On the Subject of Block Stacks

I guess dreams can come true, because this module literally came out of one of my dreams.

When the needy activates, there will be a single number on the top display and six stacks on the bottom with their size written on them. To solve the module, select three pairs of stacks in such a way that each pair of two adds up to a size which is equal to a number on the display. Each stack may only be used once. If incorrect stacks are selected, a strike will occur and the needy will deactivate.