Semiperimetro = 138/2 = 69 mm;

b + h = 69

h = 8/8;

b = 15/8;

8/8 + 15/8 = 23/8

69 = 23/8

1/8 = 69/23 = 3 mm;

h = 8/8 = 3 * 8 = 24 mm; (altezza)

b = 15/8 = 3 * 15 = 45 mm; (base);

Area = 24 * 45 = 1080 mm^2  = 10,80 cm^2;

diagonale = radice(24^2 + 45^2) = radice(2601) = 51 mm.