The 31st term of this sequence is 189.
9, 15, 21, 27, 33 (5), 39, 45, 51, 57, 63 (10), 69, 75, 81, 87, 93 (15), 99, 105, 111, 117, 123 (20), 129, 135, 141, 147, 153 (25), 159, 165, 171, 177, 183 (30), 189.
Silvia has to score a 101 to get an average of 90 for all four tests.
Explanation: 90=(86+81+92+x)/4
360=259+x
101=x
