Let the new angle of elevation of the rock after increasing the distance to 15 m be x degrees.
Since the initial angle of elevation of the cliff top from a point on the ground is 30°, we can make the following equation:
tan(30°) = height of the cliff / distance to the top of the cliff
Thus, the height of the rock will be equal to:
the height of the rock = 15 * tan(30°) = 15 * 0.5774 = 8.66 m
Now we will find the new height of the cliff after increasing the distance to the foot of the cliff to 15 m:
the new height of the cliff = 17.3 - 8.66 = 8.64 m
Now let's make a new equation:
tan(x) = new cliff height / 15
tan(x) = 8.64 / 15
x = arctan(8.64 / 15)
x ≈ 29.15°
So, the new angle of elevation of the rock after increasing the distance is 29°.