x=-2 and y=3.
The first step we take is to substitute the value for y from the second equation into the first equation:
4x+5(3x+9)=7
This is justified by substitution. The next step is:
4x+5*3x+5*9=7
4x+15x+45=7
This is justified by the distributive property. The next step is:
19x+45=7
This is justified by addition of like terms. The next step is:
19x+45-45=7-45
19x=-38
This is justified by the subtraction property of equality. The next step is:
19x/19 = -38/19
x=-2
This is justified by the division property of equality. The next step is:
y=3(-2)+9
y=-6+9
y=3
This is justified by substitution, multiplication and addition, in that order.
