There are two cars of the same model and the same mass of 1,400 kg The first (blue) car is travelling at 90 km/h and the second (yellow) car is travelling at 54 km/h. What is ratio of the KE of the first car to the KE of the second car?

The kinetic energy formula is \frac{1}{2}mv^{2}, where m is the mass and v is the velocity in km/hr.
The mass of both the objects are the same, but the velocity for the first car say v_{1}= 90 \frac{km}{hr} = 25 \frac{m}{s}
The velocity of the second car say v_{2} = 54\frac{km}{hr} = 15 \frac{m}{s}
So, we have the ratio of K.E of the two cars as
\frac{1}{2}mv_{1}^{2} : \frac{1}{2}mv_{2}^{2}
The like terms gets cancelled and we are left with v_{1}^{2} : v_{2}^{2}
Plugging in v_{1} = 25 and v_{2}= 15 we get 25^{2} : 15^{2}
= 625 : 225
= 25 : 9
So, the ratio of the KE of the first car to the KE of the second car is 25 : 9
Here is how you can convert km/hr to m/s
https://byjus.com/questions/how-do-you-convert-km-h-to-m-s/
Here is how you can express a ratio in the simplest form