Shashank, the answer to your query is 25:1 that is, the ratio of intensity of maxima to the intensity of minima is 25:1 . Now let us understand the solution of this query.

It is given that the slit widths are in ratio 4:9

Now, the width (W) is directly proportional to intensity (I), so W1/W2 = I1/I2

Therefore, we get the ratio I1/I2 = 4/9

Now, the intensity is proportional to the square of the amplitude also, so

I1/I2 = (A1)^2/ (A2)^2

So, the ratio of amplitude is A1:A2 is 2:3

Now, the intensity of maxima is  (A1+A2)^2  = (2+3)^2 = 25

and the intensity of minima is     (A1-A2)^2 = (2-3)^2 = 1

Therefore the ratio of intensity of maxima to that of minima is 25:1