Answer:
11
Explanation:
The formula for a triangular pyramid is:
V = 1/3 × base area × height
(base area is base × height ÷ 2 so x × 6 ÷ 2)
99 = 1/3 × 6x/2 × 9 divide equation by 9
÷9 ÷9
3(11 = 1/3 × 6x/2) multiple equation by 3
(33 = 6x/2) multiple by 2
66 = 6x divide by 6
÷6 ÷6
11 = x