In a given multilayer welding application, the final layer will require an average of $6\mathrm{.}4$ cu ft of acetylene and $6\mathrm{.}7$ cu ft of oxygen per linear foot of weld. The thickness of the material being welded is

A$.\frac{5}{8}$ in$.$

B$.\frac{1}{2}$ in$.$

C$.\frac{3}{8}$ in$.$

D$.\frac{3}{4}in.$