Own answer

The plotted points do seem to fit a straight line, so yes: linear.

Best fit, in this case, is a line where an equal number of plotted points are above the line, as there are below the line.

The line goes through the points $(16,57)$ and $(44,120)$. The formula is given by $H=21+2.25B$.

The difference is small.

$P=21+2.25\cdot 32=93$

Linear interpolation: $\frac{(91+94)}{2}=93$.

$V(t)=\frac{V(0)}{273}\cdot (t+273)=V(0)\cdot (\frac{t}{273}+1)$

$V\left(0\right)$ is a constant coefficient, therefore the formula can be seen as $V\left(t\right)=a\cdot t+b$.
The pressure must remain constant though. The domain is $D=[-273,\to \rangle$

Enter: Y1=1+1/273X. Window settings: $-300\le x\le 300$ and $-1\le Y\le 3$.

$V\left(20\right)=1+\frac{20}{273}=1.073$ m³

$1.5=1+\frac{1}{273}t$ leads to $t=136.5$ . So at 136.5°C.

$s\left(0\right)$ is the distance travelled at $t=0$ and $v$ is the speed in m/s.

$s\left(t\right)=20t$. Enter: Y1=20X. Window settings: $0\le x\le 50$ and $0\le y\le 1000$.

$s\left(t\right)=400+15t$, so enter Y2=400+15X.

You may use the graphic calculator. $20t=400+15t$ leads to $t=80$

In a graph you can see that it is quite reasonable to assume a linear relation: $N=300L-10000$.

$N=300\cdot 85-10000=15500$.

You may use the graphic calculator: $300L-10000=4500$ leads to $L=48$.

Yes, there is a linear relation between $L$ and $N$, so linear extrapolation is possible. The question remains whether a salmon can grow to $120$ cm though.