A rocket motor is manufactured by bonding together two types of propellants, an igniter and a sustainer. The shear strength of the bond y is thought to be a linear function of the age of the propellant x when the motor is cast. Twenty observations are shown in the table on the next page.
(a) Draw a scatter diagram of the data. Does the straight-line regression model seem to be plausible?

Age x (weeks) Strength y (psi) Age x (weeks) Observation Strength y (psi) Observation Number Number 2158.70 15.50 1 11 2165.20 13.00 12 3.75 1678.15 23.75 2399.55 2316.00 8.00 13 1779.80 25.00 2061.30 17.00 14 2336.75 9.75 4 2207.50 5.00 15 1765.30 22.00 1708.30 19.00 16 2053.50 18.00 1784.70 24.00 17 2414.40 6.00 2200.50 2575.00 2.50 18 12.50 2.00 2357.90 7.50 19 2654.20 10 2277.70 11.00 20 1753.70 21.50