Hello,

to B:

You have to calculate the volume of the concrete (without considering that concrete will shrink when it is hardening )

slab: the slab is a cuboid with the base area 7m * 7m = 49 m² and the height 0.1 m. Therefore the volume of the slabe is:V_s = 4.9 m³

footing: The measures are not clear: Is the footing 0.35 m deep or is it 0.6 m deep. I've done both possibilities.

To get the volume you first have to calculate the base area. The simplest method is to subtract an inner square from the constant outer square (see attachment)

0.6 m deep: a = 49m² - 6.3*6.3m² = 9.31 m²

V = 9.31m² * 0.6m = 5.586 m³

0.35 m deep: a = 49m² - 5.8*5.8m² = 15.36 m²

V = 15.36m² * 0.35m = 5.376 m³

price: (4.9m³ + 5.586m³) * $120/m³ = $1258.32 or

price: (4.9m³ + 5.376m³) * $120/m³ = $1233.12

EB