Express the average age of three sisters in the terms of the age a of the firstborn (in years) if the second was born 4 years after the first and the third was born 6 years after the second.

19

step-by-step explanation:

you estimate that the angle of elevation to the top of the 86th floor (the observatory) is 82 .the total height of the building is another 123 meters above the 86th floor.

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