Since the angles are bisecting < RSU = < UST
substitution----- 4x+16=9x-9
subtract 4x from both sides----- 16=5x-9
add 9 to both sides-----25=5x
divide by 5 on both sides------ 5=x
The value of x is 5
substitute the value of x in both expressions
1st expression: 4x+16
substitute the value of x------ 4(5)+16= 20+16=36
2nd expression: 9x-9
substitute the value of x-----9(5)-9=45-9=36
< RST= <RSU+<UST
<RSU=36 degrees
<UST= 36 degrees
------------------------------------you have calculated both above-------------------------------------------
m<RST= 36 + 36=72 degrees