Three squares, each with sides of 5 centimetres, are joined in a straight row so that neighbouring squares share a whole edge and none of them overlap. Enter the number of square centimetres in the area of the shape.

Explication

Each square covers 5 times 5, and three of them standing side by side cover three times that much. Treating the row as a 15 by 15 square stretches the shape in a direction it never grew, because joining squares in a line lengthens the row without making it any taller.