It works because 7 x 9 x 10 is the same thing as 7 x 90, since 9 x 10 is just 90. So basically he is just writing more but the answer will still be the same.
Answer:

Step-by-step explanation:
The window consists of a large square and 4 smaller triangles on the outside. The side length of this square is marked as 10, and therefore the area of this square is
.
The area of a triangle is given by
. Since the problem states that the overlapping squares are congruent, both legs of the triangle will be
and intersect at a
angle.
Thus, the sum of all four triangles is
.
Therefore, the area of the window is:

Answer:
48 cents
Step-by-step explanation:
Answer:
C on edge 2021
Step-by-step explanation:
Answer:
21 cent per card
Step-by-step explanation:
5.25 / 25 = .21
because 25 can be divided into the first 2 numbers