Answer:
REMEMBER:- LIKE TERMS ADDED AND UNLIKE TERMS SUBTRACTED
 same sign add
different sign subtract
sign (mathematical operation) of greater no. putted to the answer.
Step-by-step explanation: 
       1. -5y+2y.   
            = -3y            
       2. 6x+4x
           =10x
 3. -3m-8(m+1).             (distributive property)
 = -3m-8m+8×1
 = -11m+8
  4. -8(r-2)+6(r-2)
 = -8r-16+6r-12
 = -8r+6r-16-12  
         = -2r-28
  5. 9m-7m+13
 =2m+13