Answer:
105degrees
Step-by-step explanation:
Using the theorems that states that the sum of the opposite side of the quadrilateral is 180degrees, hence;
<RST + <TQR = 180
5x+15 + 4x+ 3 = 180
9x + 18 = 180
9x = 180 - 18
9x = 162
x = 162/9
x = 18
Since <RST = 5x+15
<RST = 5(18) + 15
<RST = 90 + 15
<RST = 105degrees
Hence the measure of <RST is 105degrees
