The graph of \(f'\), the derivative of the function \(f\), is shown above for \(0\leq x\leq 20\). The area of the regions between the graph of \(f'\) and the \(x\)-axis are \(15\), \(12\), and \(4\) respectively. If \(f(0)=5\), what is the maximum value of \(f\) on the closed interval \(0\leq x\leq 20\) ?