Question 697498
Volume of cube  I = 6^3= 216 cu.m

Volume of cube II = 8^3  = 512 cu.m

Volume of cube III = 10^3= 1000 cu.m

Add up
Total volume = 1728 cu.m

Volume of new cube = 1728 cu.m

length of side = cube root of 1728 = 12 

side = 12m