Answer: see below
Explanation:
3x-12=7x+8 ⇔ given
-12=4x+8 ⇔ addition property of equality
-20=4x ⇔ subtraction property of equality
x=-5 ⇔ division property of equality
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5(x-1)=4x+13 ⇔ given
5x-5=4x+13 ⇔ distributive property
x-5=13 ⇔ subtraction property of equality
x=18 ⇔ addition property of equality