Let's start by simplifying the equation given:
\[ 168 = 18r + 12(2r) \]
First, simplify \(12(2r)\):
\[ 12(2r) = 24r \]
Now substitute this back into the equation:
\[ 168 = 18r + 24r \]
Combine the like terms on the right side:
\[ 168 = (18r + 24r) = 42r \]
Next, isolate \(r\) by dividing both sides by 42:
\[ r = \frac{168}{42} \]
Now, perform the division:
\[ r = 4 \]
Thus, the solution is:
\[ r = 4 \]