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October 4, 2015
Posted by **josh** on Thursday, November 11, 2010 at 7:52pm.

- geometry -
**jai**, Thursday, November 11, 2010 at 8:44pmrecall the properties of parallelogram,,

one of the properties of a parallelogram is that the opposite angles are congruent/equal,, since you are given angles A and C, and they are opposite, equate them to get x:

4x - 57 = x + 3

combining similar terms,

4x - x = 57 + 3

*when transposing terms to other side of equation, the sign becomes the opposite,, that's why x (from right side) when transposed to left side becomes -x, and -57 becomes 57 after transposing,, simplifying this,

3x = 60

x = 20

hope this helps. :)