To find the solution you start with the greater numbers (without the sings) in the target list:
Equal sings gives +
Different sings gives -
Two numbers that multiplied equals +90 are: +9 and +10
Two numbers that multiplied equals -88 are: -11 and +8
Two numbers that multiplied equals +70 are: -10 and -7
Two numbers that multiplied equals +40 are: -8 and -5
Two numbers that multiplied equals -33 are: -3 and +11
Two numbers that multiplied equals -20 are: +5 and -4
Two numbers that multiplied equals -18 are: -6 and +3
Two numbers that multiplied equals +9 are: -1 and -9
Two numbers that multiplied equals +6 are: +1 and +6
Two numbers that multiplied equals -6 are: +3 and -2
Two numbers that multiplied equals 0 are: +7 and 0
Then, you get the next final result:
