Answer: x=4% i.e.
Rate of interest = 4% per annum.
Explanation:
Since we have given that
Amount Alex invested = £4000
Number of years = 7
Rate of interest = x%
Amount she received at the end of 7 years = £5263.73
We will use " Compound Interest " formula :

Hence, x=4% i.e.
Rate of interest = 4% per annum.