Step one is to calculate the lengths of the triangle sides. E B is a face diagonal, equal to twelve square root of two centimeters. E P is calculated as the square root of E H squared plus H P squared, which is the square root of twelve squared plus six squared, resulting in six square root of five. B P is the square root of B C squared plus C G squared plus G P squared, which simplifies to the square root of twelve squared plus twelve squared plus six squared, equaling eighteen centimeters.