You can add numbers mentally if there are zero's behind them.
Answer:
50
Step-by-step explanation:

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We make use of the special form for the difference of squares:
(a+b)(a-b) = a²-b²
Answer:
21.6 km/hr
Step-by-step explanation:
multply the speed value by 3.6
Tangent (40) = tree height / 30 feet
tree height = tangent (40) * 30 feet
tree height = 0.8391 * 30
tree height = 25.173 feet