simplify the following boolean functions a. f(a, b, c, d) = ∑ (0, 6, 8, 13, 14) d(a, b, c, d) = ∑ (2, 4, 10) b. f(a, b, c, d) = ∑ (5, 6, 7, 12, 14, 15) d(a, b, c, d) = ∑ (3, 9, 11