namely, if the consumption in 1974 was "x" or the 100%, 4300 is 54.7% extra of that, so 4300 is really 100%+54.7%, or 154.7%, now, what is "x" then?
well [tex]\bf \begin{array}{ccllll}
amount&\%\\
\textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\
4300&154.7\\
x&100
\end{array}\implies \cfrac{4300}{x}=\cfrac{154.7}{100}[/tex]
solve for "x"