So, to find the volume of just the cement part, you need to find the volume of the whole shape, then find the volume of the garden. then subtract them to find the volume of just the cement sidewalk.
volume of garden: 16 x 6 x 1 (l x w x h)= 96 ft3
volume of whole: length=16+4+4=24, width=6+4+4=14, height=1
you have to add 4 to each sides of the length and width to get the entire length.
volume of whole=24 x 14 x 1=336 ft3
now subt.
336-90=246 ft3 would be the volume of the cement walkway.
