It's dependent on the context. A book may ask you to find the f'(x) of a function and you may have to use a u sub in your problem which requires you to find the dy/dx of what you substitute. So in this case both would be used.
From the figure the given line passes through the points (0, 0) and (-4, 8).
Recall that the equation of a straight line is given by

Thus, The equation of the given figure is given by
Answer:
Amount of money Judy has in her account is
.
Amount of money Tommy has in his account is 
Step-by-step explanation:
To find : Amount of money in Judy account and amount of money in Tommy account:
Solution:
Given:
Judy has $7500 more than a number in her account.
Let the number be 'n'.
So we can say that;
Amount of money in Judy account is equal to 7500 plus number.
framing in equation form we get;
Amount of money in Judy account = 
Hence Amount of money Judy has in her account is
.
Now Given:
Tommy has 6 more than 3 times the amount of money in his bank account than Judy.
So we can say that;
Amount of money in Tommy account is equal to 3 multiplied by Amount of money in Judy account plus 6.
framing in equation form we get;
Amount of money in Tommy account = 
Hence Amount of money Tommy has in his account is
.
Use Bidmas, solve all the inner brackets (), with first division, then multiplication then addition then subtraction