Using the concept of specific heat capacities, 

heat released = heat absorbed

q = m * s * ?T

here m = mass

s = specific heat capacity

s of water = 4.2 j / g °c

?T = change in temperature

q_metal = q_water

21.5 * s * ( 100 - 27) °c = 75 * 4.2 * ( 27 - 22.5 ) °c

s = (315 * 4.5 )/ (21.5 * 73)

s = 1417.5 / 1569.5

s = 0.90 j / (g °c)