Take into account that the volume of the given figure is:
V = A·s
where A is the area of the triangular face of the figure.
Calculate A, by using the following formula:
A = b·h/2
where b is the base (b = 6 mm) and h is he height (h = 11 mm). Replace theses values into the formula for A:
A = (6 mm)(11 mm)/2
A = 33 mm²
Next, in the formula for V, solve for s and replace the previous values of A and V = 264 mm³, to obtain s:
V = A·s
s = V/A
s = (264 mm³)/(33 mm²)
s = 8 mm
Hence, the value of s is 8 mm