[A diagram shows a triangular prism standing upright on one of its triangular sides. The narrator reads out the onscreen text.]

NARRATOR: Question four. Find the surface area of the triangular prism shown in the diagram. The triangular base is a right-angled triangle with side lengths of 3, 4 and 5 centimetres. The height of the prism is 10 centimetres. We can see that this shape has five surfaces - two equivalent triangular surfaces and three different rectangular surfaces. Let's isolate those surfaces. So the total surface area would be equal to 2 times the triangular surfaces - which we know to be a right-angled triangle with side lengths of 3, 4 and 5 centimetres. And then there are three different rectangles, each with a height of 10 centimetres but one with a base length of 5, one with a base length of 4 and one with a base length of 3 centimetres. So we have two triangles. The area of a triangle is given by half times the base - which in this case is 4 - and times the height - which in this case is 3. Area of a rectangle is just base times height, so 5 times 10, plus 4 times 10, plus 3 times 10.

[The equation written onscreen is TSA = 2 x (½ x 4 x 3) + 5 x 10 + 4 x 10 + 3 x 10.]

NARRATOR: So we have 2 times half times 4 is 2, times 3 gives 6. So two triangles each with an area of 6, a rectangle with an area of 50, another rectangle with an area of 40, and another rectangle with an area of 30.

[The second equation onscreen is TSA = 2 x 6 + 50 + 40 + 30.]

NARRATOR: So we get 12 plus 120. So 132 square centimetres.