For the following cases, determine the allowable gross vertical load$-$bearing capacity of the foundation. Use Terzaghi's equation and assume general shear failure in the soil. FS $=4.$

a$)$ Strip footing: $B=4ft,D_f=4ft,{}^{\text{'}}=30,c^{\text{'}}=400l\frac{b}{f}{t}^2,y=115l\frac{b}{f}{t}^3$

b$)$ Strip footing: $B=2m,D_f=1\mathrm{.}4m,{}^{\text{'}}=32,c^{\text{'}}=0,y=17\mathrm{.}4k\frac{N}{m^3}$