A plant costs p dollars and a bush costs b dollars. Ana buys 2 plants and 4 bushes for $42. Paola buys 7 plants and 9 bushes for $107. Write down a pair of simultaneous equations and solve them to find out the value of p and the value of b.

2p + 4b = 42

7p + 9b = 107

p = $5

b = $8

Step-by-step explanation:

p is cost of plant, b is cost of bush

2p + 4b = 42

7p + 9b = 107

First we'll solve the first equation for p in terms of b:

2p + 4b = 42

subtract 4b from both sides

2p = -4b + 42

divide both sides by 2

p = -2b + 21

Now substitute that value in for p in the second equation, and solve for a numerical value of b:

7(-2b + 21) + 9b = 107

-14b + 147 + 9b = 107

combine like terms:

-5b = -40

b = 8

Use this to go back and solve for p:

p = -2b + 21

p = -2(8) + 21

p = -16 + 21 = 5

check the math:

2p + 4b = 42

2(5) + 4(8) = 10 + 32 = 42