8. finley has 152 yellow, red, and blue marbles in a bag. he has seven more red marbles than yellow marbles, and three times as many blue marbles as yellow marbles. how many yellow marbles does finley have? write an equation to represent this problem. then solve the equation. a. x + x + 7 + 5x = 152; x = 21 b. x + x + 7 + 3x = 152; x = 29 c. x + x + 7 + x = 152; x = 48 d. x + x + 7 + 2x = 152; x = 36

Let number of yellow marbles = x

Let number of red marbles = y

Let number of blue marbles = z

Given that Finley has 152 yellow, red, and blue marbles in a bag.

So we get equation:

x+y+z=152...(i)

"He has seven more red marbles than yellow marbles" means:

y=x+7...(ii)

"three times as many blue marbles as yellow marbles." means:

z=3x...(iii)

Now we just need to solve those equations to find the answer.

Plug (ii) and (iii) into (i)

x+(x+7)+(3x)=152

x+x+7+3x=152

Which looks similar to choice (B)

5x+7=152

5x=145

x=29

Hence final answer is choice B.

Required equation is

x+x+7+3x=152

Number of yellow marbles = 29