##4 meters##
Given:
##SA=208 m^2##
##L=6m##
##H=8m##
Missing:
##W=?##
substitute all the given to the formula for surface area of a rectangular prism is
##SA=2(LW+LH+WH)##
##208m^2=2[(6m)W+(6m)(8m)+W(8m)]->## substitute all given
##208m^2=2[(6m)W+48m^2+(8m)W]->## simplify.
##104m^2=(6m)W+48m^2+(8m)W->## divide both sides by 2
##104m^2-48m^2=(6m)W+(8m)W->## group all constant on the left side of the equation.
##(56m^2)/(14m)=(cancel((14m))W)/cancel((14m))->## combine.
##4m=W->## cancel and divide.
##W=4m->## apply symmetric property.