The answer is 8
Here's why:

The exponents are subtracted one from another when divided.

We can look at the problem this way:

Since we have the power of -1 on the 3, we apply this rule:

Also this rule because we have the power of 1 on the 6:

Then we get this:

We apply the rule:

We get this:
Firstly, the rate of increase of Canton = 80/7720 = 0.010
The rate of increase of HP = 120/3200 = 0.0375
Apply the formula of compound interest==> A =A'(1+i)^n
The population will be equal when the following equality is satisfied
7720(1+0.01)^n = 3200(1+0.0375)^n
or
7720x1.01^n = 3200x1.0375^n
Divide both sides by 3200 ===>(193/80)x1.01^n=1.0375^n
Step-by-step explanation:
