Question

what number should be added to -1 to get 5/7

Answer 1

-1+x=5/7
x=5/7+1
x=12/7
so -1+12/7=5/7

Answer 2

let the number x should be added in -1 to get 5/7 then 
-1 + x = 5/7
x = 5/7 + 1
x = 12/7
hence the number is 12/7