Sign and Magnitude (Hexadecimal and 8-bit

First off sorry, but I did away with the automatic formatting.

For a homework assignment I need to do a few problems which involved adding and subtracting hexadecimal and 8-bit numbers being added and subtracted. I've done the problems that involve the unsigned numbers fine, but I'm confused as to how to approach the ones that are in sign and magnitude format. The book only explains sign and magnitude for binary numbers which does not help me as I'm already familiar with them, but am not sure how to apply it for hexadecimal and 8-bit decimal numbers.

For instance one of the problems is:
part a: if A = 0D34 and B = DD17
part b: A = BA1D and B = 3617
assume the numbers are signed 16-bit hexadecimal numbers stored in sign and magnitude format. What is the sum of A and B.

now part a: A = BA7c and B = 241A
part b: A = AADF and B= 47BE

What is A-B if they represent signed 17-bit hexadecimal numbers stored in sign and magnitude format.

I'm hoping if I can get down the basics of sign and magnitude with hexadecimal numbers that I'll be fine with the rest of the homework.

I'm not asking for anyone to do the assignment, but rather just a quick lesson in how to implement sign and magnitude using hexadecimal numbers.
After more research it appears that if the leading digit is 0-7 the number is positive, but if it is 8-F the number is negative. Is this correct?

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