We are given that a house had a value of $245000 and its value was increased by 9%. To determine how much is this value increase in dollars we need to multiply the value of the house by 9/100. We get this:

Therefore, the increase in dollars is $22050. Now, to determine the current value we need to add the increase to the previous value, we get:

Therefore, the current value of the house is $267050.
You must try to remove one of the unknown variables from the system by multiplying one in a way that when adding (or subtracting) one to another “makes it disappear” and so whatever value you get can be substituted back in to get the other unknown!
Answer:
The differential equation is 
Step-by-step explanation:
Differential equation for the rate of change in radiation level:
Radiation level is R.
Rate of change indicates that the radiation level R varies in function of time t, which mathematically means that we have:

After the reactor is shut down, the radiation from the nitrogen-17 decreases in such a way that the rate of change in the radiation level is directly proportional to the radiation level.
Rate of change is k. Decreases means that k is negative. Proportional to the radiation level of R means that -k multiplies R. So the differential equation is:

1/4:3= 1/4•1/3=1/12acre - size of each section
1/2•1/5=1/10yard