Hi, to answer this question we have to apply the next formulas:
Volume of a cone: 1/3 π r² h
Where r is the radius and h is the height (unknown)
Diameter = r x 2
8 = 2r
8/2 =r
r = 4
Before calculating the volume we have to apply the Pythagorean Theorem to find h. (where the slant is the hypotenuse and h and r are the sides of the triangle)