120*28=3360 is the total amount of grass and original grass growing in 10 mu of grassland in 28 days. Divide 2 10 and 30 mu by 3 to get that 70 sheep ate 10 mu of grassland in 63 days, and the total amount of grass is 70 * 63 = 44/kloc. 44 10-3360= 1050 represents grass growing for 63-28=35 days, so the growth rate is 1050/35=30/ day, and 3360-30*28=2520 is/kloc-0. On the day of 105, the new grass quantity is 30* 105=3 150, and the total grass quantity is15120+3150 =150.