after a year, the car price dropped to £9600, already dropped by 25%, well, 100% - 25% is just 75%, therefore, £9600 is really just the 75% of the original price.
now, let's say "x" is the original price and therefor the 100%, what is it?
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
9600&75\\
x&100
\end{array}\implies \cfrac{9600}{x}=\cfrac{75}{100}\implies \cfrac{9600\cdot 100}{75}=x[/tex]
