**Acceleration Calculation:**

To find the acceleration of the car, we need to use the formula:

acceleration (a) = (final velocity (v) - initial velocity (u)) / time (t)

Given data:
- Initial velocity (u) = 18 km/hr
- Final velocity (v) = 36 km/hr
- Time (t) = 5 minutes = 5/60 hours (since we need to convert minutes to hours for consistency)

**Converting Units:**

Before we can calculate the acceleration, we need to convert the velocities and time to the same unit. In this case, we will convert everything to meters per second (m/s) to maintain SI units.

1 km/hr = 1000 m/3600 s = 5/18 m/s

So, the initial velocity in m/s is:
u = 18 km/hr * (5/18 m/s) = 5 m/s

And the final velocity in m/s is:
v = 36 km/hr * (5/18 m/s) = 10 m/s

The time in hours is:
t = 5 minutes * (1/60 hours/minute) = 1/12 hour

**Calculating Acceleration:**

Now that we have the values in the same unit, we can calculate the acceleration using the formula:

a = (v - u) / t

Substituting the values:
a = (10 m/s - 5 m/s) / (1/12 hour)

To divide by a fraction, we invert and multiply:
a = (10 m/s - 5 m/s) * (12 hour/1)

Simplifying:
a = 5 m/s * 12 hour = 60 m/hour

**Final Answer:**

Therefore, the acceleration of the car is 60 m/hour, which means the car's speed increases by 60 meters per hour.