hi

First fix the points on the co-ordinate plane. you will see that a right triangle is formed when you join the point with

i) the origin

ii) (4,0)

iii) (0,5)

Now, calculate the length of the hypotenuse of this triangle~ a simple pythagoras theorem calculation.

So you will have lengths of all three sides of the triangle~ Next use the ratios of sine, cos and tan. You will see that sin of the angle is given by the ratio of the opposite side : the hypotenuse.

Just substitute the numbers and get the answer. If you aren't able to complete, I'll upload the image bearing the right triangle.