Given: 
m/n-3(m+n)
m=-10 and n=-2 
Solving: 
-10/-2-3(-10-2) Since m=-10 and n=-2, we substitute them in for the values since they have an equal relationship. 
Now, follow Orders of Operations: PEMDAS 
-10/-2-3(-12) Simplify parentheses (P)
There are no Exponents (E) 
Multiplication (M) and Division (D) are =, so we do whatever operation comes from the left to right. 
-10/-2=5 Division comes first on the left.
therefore:
5-3(-12)
-3(12)=-36, Multiplication is last on the right.
therefore: 
5-36
5-36=-31 After M/D, we do Addition and Subtraction, which are also =, so we do them left to right. 
Therefore -10/-2-3(-10-2)=-31