(-2ц 2/3дробь -2 4/21дробь):17/21+5.1

=(2 14/21 - 2 4/21) : 17/21 + 5.1 = 10/21 : 17/21 + 5.1 = 10/21 * 21/17 + 5.1 = 10/17 + 5.1 = 10/17 + 51/10 = 767/170 или примерно 4.51