To represent Nina's savings towards earning her new phone, we need to consider the $100 she already received for her birthday and the $50 she plans to save each week.
Let \( w \) be the number of weeks.
The total amount Nina will save after \( w \) weeks is \( 50w + 100 \). She needs to save a total of $499 to purchase the phone.
Thus, the equation that represents her savings is:
\[ 50w + 100 = 499 \]
So the correct response is:
50w + 100 = 499