Answer:
The formula for compound interest is: A = P(1 + r/n)^(nt)
Where:
A = the future value of the investment (the amount Alex has at the end of 7 years)
P = the initial investment (£4000)
r = the annual interest rate (x/100)
n = the number of times interest is compounded per year (let's assume it is compounded annually)
t = the number of years invested (7)
Plugging in the given values and solving for x:
5263.73 = 4000(1 + x/100)^7
So x = ((5263.73/4000)^(1/7))-1*100
x = 6.33% (approximately)
So, the interest rate is 6.33%.