Take another look at the sentence:
Dotted with clouds, Grandma Ruth watched the birthday balloons escape her
fingers and float into the sky.
Dotted with clouds, a participle phrase, is right next to Grandma Ruth, an illogical target. The sky, not poor Grandma, should be full of clouds! Before you continue, review the rules for misplaced and dangling modifiers.
Go back to the sentence to try again.