6 is correct for this questions answer
we have

This is a mixed number
we know that
A mixed number is a combination of a whole number and a fraction.
So
is equal to

where
is the whole number
is the fraction

therefore
the answer is

3s+28=85, take away 28 from both sides of the equals to give you 3s=57, divide by 3 on both side to give you s=19.