Answer: 70 ft
Step-by-step explanation:
Given
height of book is measured by the function is

when the book is thrown 

The height of the book is 
The sum of two numbers a and b decreased by their product is (a+b)-ab
Step-by-step explanation:
Given the two numbers as a and b
Sum of these two numbers is a+b
The product of the two numbers is a*b, ab
The sum of the two numbers decreased by their product will be;
(a+b)-ab
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Keywords : sum of two numbers, product
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Answer:
12
Step-by-step explanation:
3 x 4 = 12