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a.(8.28+2.69)+4.72 =(8.28+4.72)+2.69 =13+2.69 =15.69b.(8.28+2.69)+4.72 =8.28+2.69+4.72 =10.97+4.72 =15.69c.(8.28+2.69)+4.72 =2.69+8.28+4.72 =2.69+13 =15.69