1. changing in time problem

Ok two resistors R1 and R2 are connected parallel.

Total resistance is given by $R^-1 = R1^-1 + R2^-1$
R1 is 80 ohms & increases at 0.3 ohms per sec
R2 is 100 ohms & increases at 0.2 ohms per sec
so the question is now, "how fast is R changing at that time?"

2. looks familiar ...

$R^{-1} = R_1^{-1} + R_2^{-1}$

take the time derivative ...

$-R^{-2} \cdot \frac{dR}{dt} = -R_1^{-2} \cdot \frac{dR_1}{dt} - R_2^{-2} \cdot \frac{dR_2}{dt}$

get rid of the negative exponents and isolate $\frac{dR}{dt}$ ...

$\frac{dR}{dt} = \frac{R^2}{R_1^2} \cdot \frac{dR_1}{dt} + \frac{R^2}{R_2^2} \cdot \frac{dR_2}{dt}$

you have all the info for R1 and R2 ... calculate R from the original equation and determine dR/dt.