Question: how do you subtract like terms?
Answer: Subtract xy from 10xy. Here, 10xy, xy are like terms. The difference of the coefficients = 10 - 1, [xy means 1xy] ... 
Subtract 4x from -8x. Here, 4x and -8x are like terms. ... 
Subtract -3x from -7x. Here, -3x and -7x are like terms. ... 
15x - 4x - 12y - 3y. Here, 15x and 4x are like terms. ... 
Subtract 4x + 3y + z from 2x + 3y - z.