Using the equation x – 3y = -21, create a system of equations that can be easily solved using the addition method. Include the system you created, your solution methods, and your final answer.
Please help i will give brainlist

Find the gradient of f(x,y,z)equals=left parenthesis x squared plus y squared plus z squared right parenthesis superscript negative 1 divided by 2 baseline plus ln left parenthesis x right parenthesis x2+y2+z2−1/2+ln(xyz) at the point left parenthesis negative 2 comma 1 comma negative 2 right parenthesis(−2,1,−2).

Plzzzz i beg u asap ! what is the equation of this graphed line? enter your answer in slope-intercept form in the box.

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15