[tex]\Large\boxed{\begin{array}{l}\sf A_t=2\cdot(10\cdot x+x\cdot 2x+10\cdot 2x)\\\sf A_t=2\cdot(10x+2x^2+20x)\\\sf A_t=20x+4x^2+40x\\\sf 4x^2+60x=216\div4\\\sf x^2+15x=54\\\sf x^2+15x-54=0\\\sf x^2-(3-18)x+(3\cdot(-18))=0\\\sf (x+3)(x-18)=0\\\sf x-18=0\\\sf x=18\\\sf c=10~cm~~\ell=18~cm~~h=36~cm\\\sf V=c\cdot\ell\cdot h\\\sf V=10\cdot18\cdot36\\\sf V=6480~cm^3\blue{\checkmark}\end{array}}[/tex]
