Welcome back — missed you this week. Step 1: Convert the initial velocity from kilometers per hour to meters per second. $$u = 72 \text{ km/hr} \times \frac{1000 \text{ m}}{1 \text{ km}} \times \frac{1 \text{ hr}}{3600 \text{ s}}$$ $$u = \frac{72 \times 1000}{3600} \text{ m/s}$$ $$u = \frac{72000}{3600} \text{ m/s}$$ $$u = 20 \text{ m/s}$$ Step 2: Identify the final velocity and time. The bus is brought to rest, so the final velocity $v = 0 \text{ m/s}$. The time taken is $t = 10 \text{ s}$. Step 3: Use the first equation of motion to find the acceleration. The formula is $v = u + at$. Rearrange to solve for $a$: $$a = \frac{v - u}{t}$$ Substitute the values: $$a = \frac{0 \text{ m/s} - 20 \text{ m/s}}{10 \text{ s}}$$ $$a = \frac{-20 \text{ m/s}}{10 \text{ s}}$$ $$a = -2 \text{ m/s}^2$$ Step 4: State the deceleration. Deceleration is the magnitude of the negative acceleration. Deceleration $= |a| = |-2 \text{ m/s}^2| = 2 \text{ m/s}^2$. The deceleration/retardation of the bus is $\boxed{\text{2 m/s}^2}$. Send me the next one 📸