Answer:
No solution.
Step-by-step explanation:
Graphs never collide.
(x+4) and (y+4) both have two terms..terms are separated by addition/subtraction operators
Since the number has 3 decimal places, you'll write it as:

After that, you only simplify the fraction. Since there is know way of simplifying:

Hope it helped,
Happy homework/ study/ exam!
Answering your question on "9 students can make a poster in 10 hours. How many students should join them so that they all together can make this poster in 6 hours" its 13 students
Sorry, but this problem cannot be simplified.
It stays how it is.