As the bar of aluminum is heated, you know the length of the bar increases according to
T = = 100oC - 23oC = 77 Co
L = ( 24 x 10 - 6 (Co) - 1 ) (0.80 m) ( 77 Co)
L = 1.48 x 10 - 3 m
L = 1.48 mm
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