To solve this, we are going to use the compound interest formula: 
where
is the final amount after 
years
is the initial investment
is the interest rate in decimal form
is the number of times the interest is compounded per year
For the first 4 years we know that:
, 
, 
, and since the problem is not specifying how often the interest is communed, we are going to assume it is compounded annually; therefore, 
. Lest replace those values in our formula:
Now, for the next 6 years the intial investment will be the final amount from our previous step, so
. We also know that: 
, 
, and . Lets replace those values in our formula one more time:
We can conclude that Collin will have <span>£3691.41 in his account after 10 years.</span>
where
For the first 4 years we know that:
Now, for the next 6 years the intial investment will be the final amount from our previous step, so
We can conclude that Collin will have <span>£3691.41 in his account after 10 years.</span>
