SOLUTION: A kid has 9 baseball cards. Every week he gains 4 more cards. Use the formula y=mx+b figure out how long it would take to reach 57 cards. Remember to use let statements for both th

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: A kid has 9 baseball cards. Every week he gains 4 more cards. Use the formula y=mx+b figure out how long it would take to reach 57 cards. Remember to use let statements for both th      Log On


   

Question 855078: A kid has 9 baseball cards. Every week he gains 4 more cards. Use the formula y=mx+b figure out how long it would take to reach 57 cards. Remember to use let statements for both the y and the x.
I need help with this problem. I am also supposed to graph my equation, but I am not sure how to start out the let statements, because that is where I could get the whole problem wrong. Please help me with the whole problem though. Thanks!!
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +y+ = the number of cards he has
at the beginning of week +x+
------------------------
week 0:
+y+=+0+%2B+9+
week 1:
+y+=+4+%2B+9+
week 2:
+y+=+8+%2B+9+
week 3:
+y+=+12+%2B+9+
------------------
The equation is:
+y+=+4x+%2B+9+
------------------
They want to know what +x+ is ( the week number )
when +y+=+57+
+57+=+4x+%2B+9+
Subtract +9+ from both sides
+4x+=+48+
+x+=+12+
At the end of week 12 he has 57 cards
------------------------------------
Here's the plot:
+graph%28+400%2C+400%2C+-3%2C+15%2C+-10%2C+70%2C+4x+%2B+9+%29+