At the beginning of the year, Grayson had $45 in savings and saved an additional $19 each week thereafter. Jacob started the year with $90 and saved $16 every week. Let
G represent the amount of money Grayson has saved t weeks after the beginning of
the year and let J represent the amount of money Jacob has saved t weeks after the
beginning of the year. Write an equation for each situation, in terms of t, and
determine the who has more money saved after 18 weeks.

We'll let x represent the number of weeks it will take to save enough money. If she saves $11 each week, then in x weeks she will save 11x dollars.
Add this to the 107 she has already saved, and at the end of 11 weeks she will have 11x + 107 dollars.
We want the amount saved to be equal to the price of the bike, so our equation is

11x + 107 = 173

In a word problem, writing the equation is usually the hardest part. Now we solve the equation.

Subtract 107 from both sides to get

11x = 66

Divide both sides by 11 to get

x = 6 weeks

Hope this helps ‘