The guests enjoyed their dinner and then Liz brought in a cake. The cake __________________(DECORATE) with chocolates and jellies, and it had as many candles as the number of years Carlos had reached that day. Carlos couldn’t blow them out on the __________________(ONE) try and his friends were delighted to help him.

The cake was decorated (Торт был украшен - пассивный залог, используем формулу was/were + глагол с окончанием -ed, так как decorate правильный глагол). 
on the first try (the first - используем порядковое числительное, так как он не задул свечи в первый раз).