The equation given in the question is
(5x + 2)/2 = 2x - 1
5x + 2 = 2(2x - 1)
5x + 2 = 4x - 2
5x - 4x = - 2 - 2
x = -4
So the value of the unknown variable comes out to be -4. Yes your calculation is correct it seems from the answer that you have given. I hope i have been able to help you in this regard.Only be careful about the cross multiplication part.
