First find common denominators.
their common denominator is 12. Remember that what you multiply to the denominator, you must multiply the same to the numerator
2/3(4/4) = 8/12
1/2(6/6) = 6/12
7/4(3/3) = 21/12
Remember to bring the signs.
8/12 + 6/12 - 21/12
Simplify.
(8/12 + 6/12) - 21/12
14/12 - 21/12
-7/12
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-7/12 is your answer
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hope this helps
