Given:
Population is 2005 = 35,700
growth rate = 4% = 0.04
To find:
The population in 2030.
Solution:
The general exponential growth model is
where, a is initial value, r is growth rate and t is time in years.
Let the initial year is 2005. So, number of years between 2005 to 2030 is
Putting a=35,700, r=0.04 and t=25 in the above model.
Approximate the value to the nearest whole number.
Therefore, population of the district will be about 95,170.
You problem is you don't have any problem. You have a bunch of formulas for the perimeter and area of some shapes.
As for using the formulas, usually you're given all but one of the variables and you can solve for the remaining one.
Notice how the triangle result doesn't have area as a function of a, b and c. That's called Heron's formula and is usually not taught to secondary school students. I don't like to teach it either because Archimedes' Theorem is so much better:
The sides a,b,c and area S of a triangle satisfy