The conditions of a) and b) are a trick question, because the area is changing at a constant rate.
The oil slick is circular so it's area is calculated by the formula `A=pi r^2` Pi is a constant, and we know that A is increasing at a constant rate of `150m^2/s` So the rate of change in r is a constant that would result in `A=150`
We enter the rate of change as Area to find the value of r. `150=pi r^2` We isolate the variable r and we get `r^2=150/pi` We solve for r and we get `r=sqrt(150/pi)` The radius of the oil slick is growing at the rate of `sqrt(150/pi) m/s~~6.91m/s`
I hope you were able to follow all that. The answer to each subquestion is the same. Roughly 6.91 m/s `sqrt(150/pi)` to be exact.