Implement f(a, b, c, d) = ∑m(3, 4, 5, 6, 7, 11, 15) as a two-level gate circuit, using a minimum number of gates. Use NAND gates only. Enter the equation for f and attach files of any Karnaugh maps or other work used to derive the equation. Attach a Word, PDF, or other image file of your circuit.