In order to add to a negative number but multiply to a positive number, both numbers must be negative.
With a large number such as 150, I sometimes find it helpful to factor all possible combinations.
150
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-1 × -150 ll -1 - 150 = -151
-2× -75 ll -2-75 = -77
-3× -50 ll -3-50 = -53
-5× -30 ll -5-30 = -35
-6× -25 ll -6-25 = -31
-10× -15 ll -10-15 = -25
The numbers are -6 and -25
-6 -25 = -31
-6 × (-25) = 150
I apologize for any poor formatting