Q.48 see image.................................................

actually the ans is really big to be writen here. so let me tell u the basic method:

let the center of incircle of ABC be O. then sin(OBC)= (r – 4)/(r+4) where r is the radius of ABC 

similarly sin(OAB)= (r – 1)/(r+1) and sin(OCA)= (r – 9)/(r+9)..... note that to prove all these you will need to apply elementary geometry learnt in class 9^th.

now, OBC+OAB+OCA= 180/2= 90

hence we have 4 variables: r, OBC, OAB and OCA and four eqns. so eliminate all other variables to solve for r (note that this would be a bit lengthy). 

finally you must get r= 11.