Answer:
b=2
Step-by-step explanation:
we have
9x+12y=21 -----> equation A
6x+8y=7b ----> equation B
we know that
If the system of equations have an infinite number of solutions then the equation A must be equal to the equation B
Multiply equation B by 1.5 both sides
1.5*[6x+8y[=7b*1.5
9x+12y=10.5b ----> equation C
Compare equation A and equation C
9x+12y=21 -----> equation A
9x+12y=10.5b ----> equation C
For the equations to be equal it must be fulfilled that
21=10.5b
solve for b
b=21/10.5
b=2
