Folding only adds numbers together, so the total never changes. Both strips add up to 52. Your largest target number, 40, must be a stack of several cells added together.
Hint 2: the length budget
The strip has 10 cells and the target has 3, so the folds together must remove 7 cells. A fold removes as many cells as its shorter side has.
Hint 3: the first fold
The first fold goes between cell 7 and cell 8, counting cells from the left.
Full solution
Show every fold
Fold 1 of 3
5198861536→51981496
Fold between cell 7 and cell 8. The right side flips over the left side.
Fold 2 of 3
51981496→571822
Fold between cell 4 and cell 5. The right side flips over the left side.
Fold 3 of 3
571822→5740
Fold between cell 3 and cell 4. The right side flips over the left side.