Since ABC is equilateral, all 3 sides have equal length. side AC is 8 units since side BC is 8 units.
Line BD is placed in the middle, making D the midpoint of side AC.
knowing this information we can determine that the length of DC is 4 units (half of AC)
since triangle BDC is a right triangle, we can use the side lengths in the pythagorean theorem to find the length of BD
a²+b²=c² where a & b = legs of triangle , and c= hypotenuse (longest side)
we are given the hypotenuse and found one leg so we can plug our values into the equation to find the third
4² + b²= 8²
16 + b² = 64
b² = 48
b = 
b= 4√3 or about 6.928 units
hope this helped
Subtract the volume of the water from the volume of the tank to get the total volume of the marbles.
26 liters - 20.9 liters = 5.1 liters
He has 20.9 liters of water.
He has 85 marbles that add up to 5.1 liters of volume.
To find the volume of one marble, we divide 5.1 liters by 85.
(5.1 liters)/85 = 0.06 liters
The volume of each marble is 0.06 liters.
If he uses 200 marbles, the the marbles will occupy 200 * 0.06 liters = 12 liters.
The volume of the tank is 26 liters. 12 liters of volume is occupied by the marbles. The rest of the volume is water.
26 liters - 12 liters = 14 liters