Answer:
40287600 = B. 4 x 
Step-by-step explanation:
<u>We first have to do the multiplication of the numbers given:</u>
19 * 2,120,400
=> 40287600
<u>Now we have to figure out how many digits are after the number 4:</u>
4, 0 2 8 7 6 0 0
7 digits
Meaning that we need an exponent of 7 for it to be in scientific notation, giving us with the answer B. 4 x 
3 < 3x+6
-3<3x
-1<x
3x+6<24
3x<18
x<6
-1<x<6 the book is right