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Explanation:
Consider something like 2b+6 factoring to 2(b+3). When we distribute that outer 2 back inside the parenthesis, we're multiplying that 2 by everything inside. Factoring goes in reverse of this and we divide each term of 2b+6 by the GCF 2.
The same thing applies to this current problem as well.
Divide each term by the -1.8 we want to factor out.
The results -2b and 5 will go inside the parenthesis. That's how we end up with -1.8(-2b+5)
You can use distribution to verify this
-1.8(-2b+5)
-1.8*(-2b) - 1.8*(5)
3.6b - 9