Final answer:
To find the measure of angle QRS, subtract the measures of angles SQR and RST from 180 degrees. Solve for x and substitute it into the equation to find the measure of angle QRS. The answer is 140°.
Step-by-step explanation:
To find the measure of angle QRS, we can use the fact that opposite angles in a quadrilateral add up to 180 degrees. So, we have:
Measure of angle QRS = 180 - measure of angle SQR - measure of angle RST
Substituting the given angle measures, we get:
Measure of angle QRS = 180 - (3x + 20) - (6x + 18)
Now, solve for x and then substitute the value of x to find the measure of angle QRS.
Using the given answer choices, we can determine that the correct answer is (d) 140°.