The pattern follows: x2, x2+0, x2+7.5, x2+7.5, x2+75, x2+75. Starting with 3: 3x2=7.5, 7.5x2=15, 15x2+7.5=37.5, 37.5x2=75, 75x2+75=225, 225x2=450. The term 175 breaks the pattern - it should be 225. The series alternates between pure doubling (x2) and doubling with adding 7.5 (x2+7.5).