To find out how many weeks, \( w \), it will take for Matt to save $15,000 by saving $20 each week, you can use the following equation:
\[ 20w = 15000 \]
Now, solve for \( w \) by dividing both sides by 20:
\[ w = \frac{15000}{20} \]
Calculating the right side:
\[ w = 750 \]
So, it will take Matt 750 weeks to save $15,000.