The total number of students studying Computer Science and Commerce in 2019 is 50% more than the number of students in 2021 studying:

The required figure is given below: 

Let the total number of students in 2019 be $$x$$. 

Number of Commerce students = $$15\%\ of\ x=225$$ (given)

$$x=1500$$

Number of students in 2021 increased by 20% as compared to 2019.

Total number of students in 2021 = $$1500\times\left(1+20\%\right)=1800$$

In 2019, 

Number of students in Computer Science = 21% of 1500 = 315

Number of students in Arts  = 10% of 1500 = 150

Number of students in Science = 18% of 1500 = 270

Number of students in Engineering = 20% of 1500 = 300

Number of students in Management = 16% of 1500 = 240

Number of students in Commerce = 225 (given)

In 2021, 

Number of students in Computer Science = 18% of 1800 = 324

Number of students in Arts = 12% of 1800 = 216

Number of students in Science = 15% of 1800 = 270

Number of students in Engineering = 25% of 1800 = 450

Number of students in Management = 20% of 1800 = 360

Number of students in Commerce = 10% of 1800 = 180

Total number of students studying Computer Science and Commerce in 2019 = 315 + 225 = 540

Let the number of students studying a particular subject in 2021 = $$x$$

Total number of students studying Computer Science and Commerce in 2019 is 50% more than the number of students studying a particular subject in 2021

Hence, $$x\times\left(1+50\%\right)=540$$

$$x=360$$

The required subject in 2021 is Management. 

Hence, total number of students studying Computer Science and Commerce in 2019 is 50% more than the number of students studying Management in 2021. 

$$\therefore\ $$ The required answer is D.