$1006.6$ gram.

$\mu =1008.215$ gram that is approximately $1008.2$ gram.

$\sigma =1.4607$ gram or approximately $1.5$ gram.

$0.1056\cdot 1200\approx 127$ cars.

$48.4206$ or about $48.4$ seconds.

$2.1493$ or about $2.1$ seconds.

66.87% (about 67%)

84.13% (about 84%)

There are several possibilities; for example $\mu =10.01$ and $\sigma =0.008$ will result in 99.37% of screws being accepted.

$\text{P}(l<60|\mu =m\text{and}\sigma =s)=0.875$ gives you $\frac{(60-m)}{s}\approx 1.15$.
$\text{P}(l<30|\mu =m\text{and}\sigma =s)=0.39$ gives you $\frac{(30-m)}{s}\approx -0.28$.
Therefore: $60-m=1.15s$ and $30-m=-0.28s$. Solve the equations to get $m\approx 39.5$ and $s\approx 21.0$. The values are therefore $\mu \approx 39.5$ and $\sigma \approx 21.0$.

$\text{P}(l<g|\mu =35.9\text{and}\sigma =21.0)=0.30$ gives you $g\approx 24.9$. Therefore plants up to a length of about $25$ cm are being destroyed.

$\sigma \approx 60.8$ gram

4,8%

$1006.9$ gram (about $1007$ gram)