Please help

Joy and Cullen put some money into their money boxes every week. The amount of money (y), in dollars, in their money boxes after a certain amount of time (x), in weeks, is shown by the equations below:

Joy: y = 30x + 20
Cullen: y = 20x + 90

After how many weeks will Joy and Cullen have the same amount of money in their money boxes, and what is that amount?

6 weeks, $150
230 weeks, $7
7 weeks, $150
7 weeks, $230

Question

Please help

Joy and Cullen put some money into their money boxes every week. The amount of money (y), in dollars, in their money boxes after a certain amount of time (x), in weeks, is shown by the equations below: 

Joy: y = 30x + 20 
Cullen: y = 20x + 90 

After how many weeks will Joy and Cullen have the same amount of money in their money boxes, and what is that amount?

 6 weeks, $150
 230 weeks, $7
 7 weeks, $150
 7 weeks, $230

anonymous · Answer

@jim_thompson5910

jim_thompson5910 · Answer

y = 30x + 20 

20x + 90 = 30x + 20 ... Replace y with 20x+90

20x + 90 - 90 = 30x + 20 - 90 ... Subtract 90 from both sides.

20x + 0 = 30x - 70

20x = 30x - 70

20x = -70 + 30x

20x - 30x = -70 + 30x - 30x ... Subtract 30x from both sides.

-10x = -70 + 0x

-10x = -70

x = ???

anonymous · Answer

7 ? @jim_thompson5910

jim_thompson5910 · Answer

x = 7, yep

jim_thompson5910 · Answer

now plug that value of x into either original equation to find y

anonymous · Answer

ok

jim_thompson5910 · Answer

I recommend you do both equations to see that it's actually the solution

anonymous · Answer

y = 230 for both @jim_thompson5910

anonymous · Answer

Oh I understand it now it would be D. 230 dollars and 7 weeks, Thank you.

jim_thompson5910 · Answer

x = 7 and y = 230, correct