How to solve this sum quickly

[Darshan]

I don't know how to solve this sum within 1 min, otherwise I'll just skip it.

[Harish]

Use digital sum.

[Murali]

Use the digital sum method. You can check Aditya Ranjan's maths class on YouTube for a tutorial.

[Jasmin]

Try using the digital sum method.

[Tanuja]

Can anyone tell me which app this is? Please.

[Aftab]

It got done easily in 1.5 min.