Question

Random Acts of Kindness Day will be observed by washing windshields at the local gas station. Rewrite the sentence using active voice.

Answer 1

The answer to your question would be that in the active voice the sentence would be the following: Washing Windshields at the local gas station will observe the Random Acts of Kindness Day.

In most English sentences with an action verb, the subject performs the action denoted by the verb. Because the subject does or acts upon the verb, the sentences are said to be in the active voice.

Answer 2

The sentence
"Random Acts of Kindness Day will be observed by washing windshields at the local gas station" is in Passive voice since the object of the sentence is supposedly the subject.

Here's the active voice form.

The washing windshield will be observed the Random Acts of Kindness Day at the local gas station.