1. The township of brock is growing at a rate of 6.5% per annum. How many people are there in brock township now, if there will be 15000 in 4.5 years?
Since this is "per annum" growth (that is, with time periods of one year) rather than "continuously", you may be expected to use the compound-interest formula, A = P(1 + r/n)^(nt). In this case, A = 15,000, r = 0.065, n = 1, and t = 4.5. Solve the equation for the value of t.
2. If the population of bacteria doubles every 30 min, how long would it take for the population to triple?
You can use A = Pe^(rt) in the manner explained here
In particular, use the half-life information (in this case, the doubling-time information) to find the growth constant: P = 1 (100% of the original amount), A = 2 (200% of the original amount), and t = 0.5 (half an hour, or you could use "30" for "thirty minutes"). Then solve for the value of r.
Then plug back into the formula, using P = 1, A = 3, and the value you found for r. Solve for t.