Answer:
4 parameters are necessary to specify all solutions and correspond to the number of free variables of the system.
Step-by-step explanation:
Remember that the number of free variables of a system is equal to m-rank(A) where m is the number of unknowns variables and A is the matrix of the system.
Since the system is consistent and the rank of the matrix is 3 then echelon form of the augmented matrix has two rows of zeros.
Then m-rank(A)=7-3=4.
If it take some x minutes to upload some y digital photographs, it means it has an average of: x/y minutes to upload a single digital photograph. Then, to upload z photographs, you just multiply x/y by z.
Spoilers for answer:
If it take 7.2 minutes to upload 8 digital photographs, it means it has an average of: 7.2/8 = 0.9 minutes to upload a single digital photograph. This means that, by this rate, it will take 20 * 0.9 = 18 minutes to upload 20 photographs to the website.
