Answer:
b=2
Step-by-step explanation:
9x + 12y = 21
6x + 8y = 7b
To have an infinite number of solutions, the two equations must be equal
Take the first equation and divide by 3, since it is a factor of all the terms
9x/3 + 12y/3 = 21/3
3x+4y = 7
Then multiply by 2 to get the x term equal
2*3x + 2*4y = 2*7
6x +8y = 7*2
Comparing this to the second equation
6x + 8y = 7b
b must equal 2
