Answer:
ummmmmm peace out
Step-by-step explanation:
D = k + 20
j = 3k - 120
d = j
k + 20 = 3k - 120
20 + 120 = 3k - k
140 = 2k
140/2 = k
70 = k.....so Katie weighs 70 lbs
David and Johnathan each weigh 90 lbs
Answer: The determinant of the coefficient matrix is -15 and x = 3, y = 4, z = 1.
Step-by-step explanation: The given system of linear equations is :

We are given to find the determinant of the coefficient matrix and to find the values of x, y and z.
The determinant of the co-efficient matrix is given by

Now, from equations (ii) and (iii), we have

Substituting the value of y and z from equations (iv) and (v) in equation (i), we get

From equations (iv) and (v), we get

Thus, the determinant of the coefficient matrix is -15 and x = 3, y = 4, z = 1.
I have solved some examples in the picture
If anything is unclear let me know.
:)