Question 124457
(25d/2d-10)+(5d/10d-50) 
=12.5-10+.5-50 d's cancel out. Using decimals instead of fractions obviates the need for using fractions.
-60+13=-47
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(t^2-81)and(t^2+17t+72)
t^2-81=(t+9)(t-9)
t^2+17t+72=(t+9)(t+8)
t+9=LCM
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Ed