The answers you could use are both the second and the forth. But mostly the fourth.
Answer: 600 dollars
Step-by-step explanation: 75% is 3/4 so you divide 450 by 3 to get 150. So you know for 1/4 the price is 150 dollars. Now that you know that you can multiply 150 4 times to get the full amount. 150*4=600
The answer to the selceted problem 23/50
<u><em>Answer:</em></u>
a. He will have to read half an article per night
b. Fraction of the reading assignment read each night = 
<u><em>Explanation:</em></u>
<u>Part a:</u>
<u>We are given that:</u>
number of articles to read = 4 articles
number of nights = 8 nights
To get the number of articles that he should read per night, we will simply divide the the number of articles by the number of nights
<u>Therefore:</u>
number of articles to read per night =
articles per night
<u>Part b:</u>
Now, we know that he will read half an article each night from a total of 4 articles
To get the fraction of the reading assignment read each night, we will divide the number of articles read each night by the total number of assignments
<u>Therefore:</u>
Fraction of the reading assignment read each night = 
Hope this helps :)
4/5y + 3(2/5x + 7/5y)...distribute thru the parenthesis
4/5y + 6/5x + 21/5y ...combine like terms
25/5y + 6/5x.....reduce
5y + 6/5x