In a laboratory experiment, you have a capacitor with a fixed capacitance of 40 nF and a variable capacitance that can be adjusted between 10 nF and 100 nF. Your task is to arrange the two capacitors in a circuit to obtain an equivalent capacitance of 24 nF. Determine how the two capacitors should be connected (in series or parallel) and what value the variable capacitance should be set to.