Thanks to my mother's help, I was able to buy a mountain bike.
Literal
Mother [possessive-の] assistance [thanks-to-のおかげで], I [topic-は] mountain-bike [object-を] buy [able-to-ことができた]
のおかげで = 'thanks to' — marks a positive cause. ことができた = the formal potential in past tense. 援助 (えんじょ) = assistance/support — a more formal word than 手伝い.