volume of this reservoir?

$\mathrm{.}2$ Assuming unit formation width, determine the average porosity for the fol$-$

lowing system when ${}_a=0\mathrm{.}20,{}_b=0\mathrm{.}11,{}_c=0\mathrm{.}29,L_1=0\mathrm{.}35L,$ and $h_a=h_b=$

$0\mathrm{.}5h_c.$

L