Question 239731
Hello, 
With this problem we can make two different equations. One equation can look like this where x will be the white sweatshirts and y will be the yellow sweatshirts.
x + y = 30  The other equation will look like this: 
9.95(x)+ 10.50(y) = 310.60  We can solve this by substitution. Make the first equation like this: 
x=30-y  Then we plug this into the second equation.
9.95(30-y)+10.50(y)= 310.60  Notice we have just y so we can solve this:
298.50-9.95y+10.50y = 310.60  Combine like terms.
298.50+.55y=310.60       Subtract 298.50 from both sides.
.55y=12.10         Divide each side by .55
y=22   We're almost there. So we know there are 22 yellow sweatshirts. Plug this into the first equation and we'll find that there are 8 white sweatshirts.
Now to check to see if these are correct you can plug these answers into both equations and they should work out. 
RJ Toftness
www.math-unlock.com