Remember that
In an inscribed quadrilateral, opposite angles are supplementary
so
B+Y=180 degrees
A+C=180 degrees
B+Y=180
substitute given values
(a+16)+(a-18)=180
solve for a
2a-2=180
2a=182
a=91
Find the measure of each angle
B=a+16=91+16=107 degrees
A=a+30=91+30=121 degrees
Y=a-18=91-18=73 degrees
C=180-A=180-121=59 degrees
