You have the following equation:
3(2x-5)-x = -7(x+3)
In order to solve the previous equation, you proceed as follow:
3(2x-5)-x = -7(x+3) apply distribution property to eliminate parenthesis
(3)(2x) + (3)(-5) - x = (-7)(x) + (-7)(3)
6x - 15 - x = -7x - 21 simplify like terms left side
5x - 15 = -7x - 21 add 7x both sides
5x + 7x - 15 = - 21
12x - 15 = -21 add 15 both sides
12x = -21 + 15
12x = - 6 divide by 12 both sides
x = - 6/12
x = -1/2
Hence, the solution for x in the given equation is x = -1/2