Explanation:
If you want to multiply a parenthesis by a number, you simply distribute the number to all the terms in the parenthesis.
So, if you want to multiply the parenthesis
(3x−7) by 5, you need to multiply by 5
both 3x and −7.
We have that 5⋅(3x)=5⋅(3⋅x)=(5⋅3)⋅x=15x and −7⋅5=−35
So, 5(3x−7)=15x−35