Can u explain how to understand in these sums whn to tk tan c and when to tk sin c in the right angld triangle?? 

Hello Akshata

It depends on the sides of the right triangle you have.

Please check this post - sin cos tan 

So, 

1. If we have height and hypotenuse, use sin
2. If we have base and hypotenuse, use cos
3. If we have height and base, use tan

Like, in this question https://www.teachoo.com/1805/535/Ex-9.1--5---A-kite-is-flying-at-a-height-of-60-m-above/category/Ex-9.1/

We have Height of 60m, and we need to find AC i.e. Hypotenuse.

So, we use sin.

If we had to find BC i.e. base ,

we would use tan.