0=40-10t-5t^2
t^2+2t-8=0
(t+4)(t-2)=0
t=-4 (not a solution) or t=2
Answer: after 2 seconds
(1 & 2/3) ft = (1 ft) + (2/3 ft)
(1 & 2/3) ft = 12 inches + 12*(2/3) inches
(1 & 2/3) ft = 12 inches + 8 inches
(1 & 2/3) ft = 20 inches
If the tree grows 5 inches per year, then it will take 4 years to get to 20 inches since 5*4 = 20. You can also divide to get 20/5 = 4.
So it takes 4 years for the tree to grow 1&2/3 feet tall.
This is all percentages so...
4/9 = 44%
2/7 = 29%
1/10 = 10%
Total = 83%
So 17% of 630 is left over which = 107
