The solids are similar. Find the volume V of the red solid.

The height of the blue pyramid is: \(\frac{5292 \cdot 3}{21^2} = \frac{15876}{441} = 36\)

\(\frac{21}{7} = 3\) which means the height of the red pyramid is just \(36\div 3 = 12\)

This means the area of the red pyramid is: 
\(\frac{1}{3} \cdot 7^2 \cdot 12 = 4 \cdot 49 = 196\)

 

Which means your answer is 196 mm³