The answer would be -1 10/11.
convert 5 1/4 to improper fraction
simplify 5 4 to 20
simplify 20 + 1 to 21
convert 2 3/4 to improper fraction
simplify 2 4 to 8
simplify 8 + 3 to 11
21/-4 4/11
21 4 over -4 11
84 over -4 11
84/-44
21/-11
convert to mixed fraction ( -1 10/11 )
