⇒ 
1) a/16 + x/16 =(a+x)/16
2) 5m/n - 3m/n =2m/n
3) 3x +4y/12 - x+2y/12 =2x+6y/12=2x+y/2
4) a+2b/2c - a-4b/2c =b/c-2b/c=-b/c
5) a-8/a^2-25 + 13/a^2-25 =a-8/(a+5)*(a-5)
6) 5x+1/2 - x/2 =9x/2+1/2=4,5x+1/2
7) a+3/4 - a+1/4 =4/4=1
8) 2x/a-b - x/b-a =2x/a-b + x/a-b=3x/a-b
9) a/x-1 + b/1-x =a/x-1 - b/x-1=a-b/x-1
10) a-5/a-3 + a+5/3-a =a-5/a-3 - a+5/a-3=(a-5)*(a+5)/a-3=(a^2-25)/a-3
11) 3x-2/5 + 5x-3/3 =(9x-6+25x-15)/15=(24x-21)/15=3*(8x-7)/15=(8x-7)/5
12) 2m+5/6 - m-a/8 =m+(20-6a)/24=m+2*(10-3a)/24=m+(10-3a)/12
13) 7/10a -5/4a =(70-25)/20a=45/20a=9/4a
