5.04*6.5-2.76
= ( 5 + 0.04) * 13 / 2 - 2.76
= (5 * 13 + 0.04 * 13) /2 - 2.76
= (65 + 0.52) /2 - 2.76
= 65.52 /2 - 2.76
= 32.76 - 2.76
= 30