$m=\frac{ -3-5 }{ \left( -5 \right)-\left( -3 \right) }$
Remove unnecessary parentheses$m=\frac{ -3-5 }{ -5-\left( -3 \right) }$
When there is a $-$ in front of an expression in parentheses, change the sign of each term of the expression and remove the parentheses$m=\frac{ -3-5 }{ -5+3 }$
Calculate the difference$m=\frac{ -8 }{ -5+3 }$
Calculate the sum$m=\frac{ -8 }{ -2 }$
Cancel out the common factor $-2$$m=4$