Question 1110865
x is some two digit number with t as the tens digit and u as the units digit
So this means,
x = 10t+u
Example: t = 5 and u = 3, so x = 10t+u = 10*5+3 = 53


In contrast, 
y = 10u+t
because the tens and units digits have been swapped


Subtract x and y
x-y = (10t + u) - (10u + t)
x-y = 10t + u - 10u - t
x-y = (10t - t) + (u - 10u)
x-y = 9t - 9u
x-y = <font color=red>9(t-u)</font>


Which is why <font color=red>the answer is choice A</font>