Step-by-step explanation:
1/2+-1/3=1/1.
1/2+1/3=1/5
1/1-1/5=1/4
1/1+1/5=1/6 add by value
1/4+3/4=3/8 add
1/6+3/4=3/12 add
3/8+3/12=3/20 then minus it on 1/4=3/16