Find the missing term.1, 6, 15, ?, 45, 66, 91

The correct answer is Option (4) → 28

The differences between the terms grow by 4 each time:

• \(6-1=5\), \(15-6=9\), so the next difference is 13: \(15+13=28\)

• The series continues \(28+17=45\), \(45+21=66\), \(66+25=91\), which fits the terms given