So to get the volume, you're going to multiply all three together, but you have to make all the units the same first. The answer wants ft³, so you want to convert them all to feet.
height = 109 ft, so that's fine already. Awesome.
width = 710 yd, but that's an easy conversion to feet. Three feet equal one yard, so just multiply (710 yd) by (3 ft/1 yd) and that'll give you the width in ft.
length = 634 m
This one is a little tricker, but same principle. First convert meters to centimeters, like this: (634 m)(100 cm/1 m). Then take that number in cm and convert it into inches, knowing that 1 inch = 2.54 centimeters. So multiply the inches you have by (1 in/2.54 cm). Then you'll change that number into feet by dividing it by twelve, since there are twelve inches in each foot.
Now you have all three measurements in feet. Just multiply them together to get the volume in ft³ and you're good to go! :)
