Without further information, all we can do is simplify:
4c + 4d = 4(c + d)
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3c - 4d = 6d + 4c Subtract 4c from both sides: -c - 4d = 6d Add 4d to both sides: -c = 10d or c = - 10d
4d + 7 = -15 so 4d = -22 so that d = -5.5
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4d is time...any moving object is 4d
there is no 4d known to man