Let [tex]A[/tex] denote the event that a child has an allowance, and [tex]B[/tex] that a child does chores.
The definition of conditional probability says that
[tex]\mathbb P(B|A)=\dfrac{\mathbb P(B\cap A)}{\mathbb P(A)}[/tex]
Assuming the events are independent, you could expand the numerator as [tex]\mathbb P(B\cap A)=\mathbb P(B)\times\mathbb P(A)[/tex]. Otherwise, you would need to know that exact probability.
You're given that [tex]\mathbb P(A)=46\%[/tex], while [tex]\mathbb P(B\cap A)=21\%[/tex].
So, the desired conditional probability is
[tex]\mathbb P(B|A)=\dfrac{21\%}{46\%}\approx45.65\$[/tex]
