Answer:
3200 cm^3
Step-by-step explanation:
1. Calculate the sides of the right triangle to get the height
We know that side c = 26 and the shortest leg is 10 cm (20cm/2) because this right triangle splits the 20cm in two)
[tex]10^{2} + b^{2} = 26^{2}   \\100 + b^{2} = 676\\b^{2} = 576 \\b = \sqrt{576} \\b = 24[/tex]
a = 10, b = 24, c = 26
2. Use the formula for the volume of a square pyramid now that you have the height (which is b) 
[tex]V = a^{2} \frac{h}{3}  \\\\V = 20^{2} * \frac{24}{3} \\V = (400)(8)\\V = 3200 cm^{3}[/tex]
V = 3200 
I hope this helped! :)