Answer:
[tex]x = -2 \\y = 3[/tex]
Step-by-step explanation:
The first step when using substitution is that you need to isolate one of the variables in one side, as it is already done with [tex]y[/tex]. Now that we have the [tex]y[/tex] value, we can move on and substitute on the other equation:
[tex]4x+5y = 7\\4x + 5(3x+9)=7\\4x + 15x+45=7 \\19x = -38\\x = -2[/tex]
And now that we have the value of [tex]x[/tex] we can substitute on the second one and find the value of [tex]y[/tex].
[tex]y = 3x +9\\y = 3 \times (-2) + 9\\y = -6 + 9\\y = 3[/tex]
And now, to double check if everything is right, we can use one of the two equations to proof that both results are correct:
[tex]4x+5y= 7 \\4 \times (-2) + 5 \times (3) = 7 \\-8 + 15 = 7 \\15-8 = 7[/tex]
This means that our results are correct!
