You can put this solution on YOUR website!
this looks like a straight polynomial division type of problem.
you are dividing a-5 into a^2 - 21
divide a into a^2 to get a
multiply a-5 by a to get a^2 - 5a
subtract a^2 - 5a from a^2 - 21 to get 5a - 21
divide a into 5a to get 5
multiply a-5 by 5 to get 5a - 25
subtract 5a - 25 from 5a - 21 to get + 4
your answer is a + 5 with a remainder of 4.
a + 5 is the quotient.
4 is the remainder.
if you multiply a - 5 by a + 5, you will get a^2 - 25.
if you then add the remainder of 4 into it, you will get a^2 - 21.
this looks to me like it is straight polynomial division.
if you are unfamiliar with how to do polynomial division, let me know and i will send you instructions.