Subtract like terms. Terms with x subtract from terms with x and constants from constants. Step one is distribute the - sign (which is really multiplying by -1) in the second binomial. In other words, multiply both terms by -1.
(11+4d)-(3-6d) = 11 + 4d -3 +6d (-1 * 3 = -3 and -1 * -6d = +6d). Now combine the terms with d and the constants.
11 + 4d -3 +6d = 8 - 10d.
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