Add the numbers 1 through 9 into the grid (only use 1 of each number) so the calculations work out and equal the numbers off the grid.
Note, BIDMAS/PIMDAS is ignored: A + B × C is the same as (A + B) × C, working left to right, top to bottom.
Hint: a good place to start is look for lines where the answer is a semi-prime with a multiplication sign (one of the factors has to be on the side with one space)
Live DEMO : https://ulikgames.github.io/Math-Square/