A = {3, 4, 7, 9}
B = {8, 9, 10, 11}
C = {4, 9, 11, 13, 15}
A∩(B∪C)
First let's solve parentheses, we want the union between B and C.
B∪C = {4, 8, 9, 10, 11, 13, 15}
Now we want the interception between A and this, which means we want just the value which appears in both.
A∩{4, 8, 9, 10, 11, 13, 15} = {4, 9}
