what rational number should be added to -5/11 to get -7/8

what rational number should be added to -5/11 to get -7/8

let the required number is x.

According to the question,

-5/11+x=-7/8

Or, x=-7/8+5/11

Or, x=(-56+40)/88

Or, x=-16/88

Or, x=-2/11

Required number=-2/11