suppose that ma is 8.1 kg and mbis 6.5kg. the distance between their centers is 0.5o m. calculate the force of attraction between these two bodies?

Somewhere in your book or your notes, you must have met the formula for the
gravitational attraction between two bodies.  If you can go back and find it, you
only need to plug your numbers into that formula, and out will pop the answer.

Formula:                            Force = G (mA x mB) / (distance)²

If everything is in SI units, then        G = 6.67 x10⁻¹¹ newton-meter² / kilogram²

You said that
                         mA = 8.1 kg
                         mB = 6.5 kg
                 distance = 0.5 m .

   Force = (6.67 x 10⁻¹¹ nt-m²/kg²) (8.1kg x 6.5kg / (0.5m)² =

                (6.67 x 10⁻¹¹ nt-m²/kg²)    ( 52.65 kg² ) / (0.25 m²) =

                     1.4047 x 10⁻⁸ newtons .

That's roughly    5.052 x 10⁻⁸ ounce .  (5% of one micro-ounce)

Alinear relationship would look like a straight line on the graph. it could have a positive negative or 0 slope. so it could be a line potentially going in any direction but it must be perfectly straight.