This is the solution to Crease puzzle #17. The puzzle gives you a strip of 7 numbers and asks you to fold it 2 times to reach a strip of 4 numbers.
Folding only adds numbers together, so the total never changes. Both strips add up to 35. Your largest target number, 12, must be a stack of several cells added together.
The strip has 7 cells and the target has 4, so the folds together must remove 3 cells. A fold removes as many cells as its shorter side has.
The first fold goes between cell 6 and cell 7, counting cells from the left.