I made a little equation solver for questions like 1_2_3_4_5=6. The numbers are already there; the puzzle is deciding which operations go in the spaces.
The code recursively builds combinations of plus, minus, multiply, and divide, puts each combination between the numbers, and evaluates the result. For the default example, it finds answers such as 1 + 2 * 3 + 4 - 5 = 6. There is also an option to print all the attempts if I want to see what it tried.
It is brute force, not symbolic algebra. The order of the numbers stays fixed, and it uses normal JavaScript operator precedence rather than trying every possible arrangement of parentheses. Non-integer results get rounded for the comparison. For a small puzzle, simply trying the combinations is a lot easier to write than a very clever solver.