For the above figure, the formula is,
x² = WY (YV + WY)
WY = 5
YV = 12
Substituting in the above formula,
x² = 5 x (12 + 5)
x² = 5 x 17 = 85
x² = 85
⇒ x = √85 = 9.21954 = 9.220
Multiply the price of each by the quantity purchased, add those together, then multiy the total by the sales tax.
Total = 1.05(3.99p + 2.50b)
Let x equal the amount of yellow marbles
Yellow = x
Purple = 3x - 8
The amount of purple marbles is than ().
Your Equation: x + 3x - 8 = 64
Solve:
x + 3x - 8 = 64
4x - 8 = 64
4x = 64 - 8
4x = 46
x = 18
x = 18, x is the amount of yellow marbles you have.
So you have 18 yellow marble.
Remember in the question it says the amount of purple marble is .
Which is: 3x - 8
So now you will plug in 18 for x and solve
3(18) - 8
54 - 8
= 46
So, you have 46 purple marbles and 18 yellow marbles
(I hope I made this helpful, easy to follow and understand.)