Is y=4x-10 a direct variation

NO. It is not a direct variation.

Direct variation is a relationship between two variables, y and x, where y is directly dependent on the changes in x with the same factor.

Direct variation equation is: y = kx; where k is a constant number.

for the above equation to become a direct variation it must be:

y = 4x or y = 4x - 0

No, since you do not divide.