You have to find the area of each separate face of the box and then add them all up.
The front and back would be ; (length x height) x 2
So;
(20 x 30) x 2
= 1200 cm^2
Then calculate the area of the top and bottom of the box;
(Width x Length)
(5 x 20) x 2
= (100) x 2
= 200 cm ^2
And finally the sides of the box:
(Width x Height) x 2
(5 x 30) x 2
= 300 cm^2
Now add all of the individual areas up to find the total surface area of the cereal box:
1200 + 200 + 30
= 1700cm^2 in total
