Question

1. if point (r, -3) lies on the line whose equation is 3x + y = 18, then the value of r is:

Explanation:

Step1: Substitute point into equation

Substitute $x=r$, $y=-3$ into $3x+y=18$:
$3r + (-3) = 18$

Step2: Simplify the equation

Simplify left-hand side:
$3r - 3 = 18$

Step3: Isolate the term with $r$

Add 3 to both sides:
$3r = 18 + 3$
$3r = 21$

Step4: Solve for $r$

Divide both sides by 3:
$r = \frac{21}{3} = 7$

Answer:

7