Two similar pyramids have corresponding dimensions in the ratio 3:5 Find the ratio of their volumes

Ineed to learn how to solve this problem

Ican figure out 20 shares multiply by $117.98 =2359.6920 shares multiply by $124.32=2486.40then take 40 shares multiply by $128.48=5139.20after that i'm lost any be greatly appreciated.

Find the constant of variation for the relation and use it to write an equation for the statement. then solve the equation.