The distance formula is given by

Take point A(0, -7) as (x₁, x₂) and point B(8, 8) as (y₁, y₂)
Distance AB =

Distance AB =

Distance AB =

Distance AB = 17
The line AB is dilated to A'B' by scale factor of 2, it means the length of the line is multiplied by 2
Distance A'B' = 2 × 17 = 34 units