A matrix is diagonal if

In other words, you want non-zero elements only when the indices of the row and the column are the same: the first element of the first row must be non zero, the second element of the second row must be non-zero, and so on. All other elements must be zero.
Her change will be $16.22 since 20 +20 is 40 and 40 - 23.78 is 16.22
4.5(8 - x) + 36 = 102 - 2.5(3x + 24)
36 - 4.5x + 36 = 102 - 7.5x - 60
72 - 4.5x = 42 - 7.5x
-4.5x + 7.5x = 42 - 72
3x = - 30
x = -30/3
x = -10 <===
Hope this helps!
Answer:
The resistance is 7.5 ohms
Step-by-step explanation:
V = IR
V = voltage I is the current and R = resistance
120 = 16*R
Divide by 16 on both sides
120/16 = 16R/16
7.5 = R
The resistance is 7.5 ohms