a mouse has a constant speed 2m/s. after 20s, a cat moves with a speed 4m/s. Find the time whn cat catch mouse?

I'm not giving the answer in proper mathematical language to make you understand it better.

Speed of rat = 2m/s

Distance covered after 20s = 40m

Time taken by cat to cover 40m = 40/4 = 10s

So, after 30s (20+10), the rat has covered 60m and the cat has covered 40m.

After 10 more sec., the rat would have covered 20m more. So the total is 80m.

The cat would have covered 40m. So the total is 80m

Thus, the cat would catch the mouse in (30+10) = 40 seconds (after the start by mouse).

If you want the time after when the cat started, then it would be 20 seconds.

The cat is moving at 2m/s faster than the mouse. After 20s the mouse is 40 m in front of the cat.

So the cat travelling at 2m/s against a stationary mouse has to travel 40m = 20 sec