How to find the orthocenter of a obtuse triángulo

Used Area from bottom box (green)= All 4 vertical faces +EFGH-IJKL
=(20*6+6*6+20*6+6*6)+20*6-14*6= 348 Square inches ...(i)

Used Area from middle box (Blue)= All 4 vertical faces +MNOP-QRST
=(14*6+6*6+14*6+6*6)+14*6-8*6=276 square inches...(ii)

Used Area from top box (Brown)= All 4 vertical faces +UVWX
=(8*6+6*6+8*6+6*6)+8*6=216 square inches...(iii)

so the surface area of the cake to be covered= 348+276+216=840 square inches.

given that 1 can covers 250 square inches

so number of cans needed = 840/250=3.36

which means 4 cans needed.