Arin has $520 and is earning $75 each week babysitting.

Write an algebraic expression

75x+520. The 520 is what she already has so it must be added to whatever she makes every week. The week is represented by the x. We don't know how many weeks she has worked, so we leave it as an unknown variable, x! The rate of pay for every week is 75, so we multiply that to the weeks, x.