Alright, these are confusing at first, I totally get it.
So, let's say I have $50 in the bank and I save $10 per week. What does that look like after 6 weeks? The $50 was there, so it's constant and doesn't change. What changes is the amount of money I've added to it.
50 + 10(6) = 50 + 60 = $110 in my account.
Now, let's look at your problem. Jesse starts with $20 and saves $3 per week. The $20 was already there and we are adding 10 weeks of $3 per week, right?
20 + 3(10) = 20 + 30 = $50 in Jesse's account after 10 weeks.
What about Juan?
15 + 4(10) = 15 + 40 = $55 per week.
Well, I bet you can figure out the rest! Good luck!