Ignore the boxes of yellow yarn, they're insignificant.
If each box has 25 balls in it, you would multiply the number of boxes by 25
First do the red balls: 7 x 25= 175
Then the blue: 12 x 25= 300
Now you add the red balls and the blue balls.
They ordered 475 balls of blue and red yarn. Or 300 blue and 175 red