Compute the sum to simplify C :
Now, 
is the entry of the matrix in row i and column j, so
-9(y + 12) = 4(-7y -8)
Use the distributive property:
-9y - 108 = -28y -32
Add 32 to both sides:
-9y - 76 = -28y
Add 9y to both sides:
-76 = -19y
Divide both sides by-19
Y = 4
Answer: He made $90 last week.
Assumption :
Let, Luis made $X last week.
He made $72 this week which is 80% of $X that he made last week
⇒ X * 80% = 72
⇒ X * 80/100 = 72
⇒ X = (72 * 100)/80
⇒ X = 90
Therefore, he made $90 last week.
To remember :
While solving this type of problems, be careful to understand which one of last time and current time is not given; just assume that one and input other conditions, the problem will be solved.
Step-by-step explanation:
The cross-section of a square pyramid will be a square. The section above the cross-section taken will basically be a similar but smaller square pyramid. D is the correct answer.
