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Look for integers that divide into 75 bearing in mind that they can be negative.
Good question and good hint. Observe factors of 75 are: 3x5x5. we need to have 5 factors so -1x1x3x5x5 now the product is negative also x,y,z,m,n should be different thus consider 5 and -5 as factors; 1x-1x3x5x-5 Now you can take it further.