3) Solve each linear system using the method of substitution. a) l_(1):y=2x+4 l_(2):x-4y=-9 b)

## Step 1: Substitute $y$ in $l_2$<br />### The first equation, $l_1$, expresses $y$ in terms of $x$. Substitute this expression for $y$ into the second equation, $l_2$. This gives us an equation with only $x$.<br /><br />## Step 2: Solve for $x$<br />### Substitute $y = 2x + 4$ into $x - 4y = -9$:<br />$x - 4(2x + 4) = -9$<br />$x - 8x - 16 = -9$<br />$-7x - 16 = -9$<br />$-7x = 7$<br />$x = -1$<br /><br />## Step 3: Solve for $y$<br />### Substitute the value of $x$ ($x = -1$) back into either of the original equations. Using $l_1$ is easier:<br />$y = 2(-1) + 4$<br />$y = -2 + 4$<br />$y = 2$<br /><br />## Step 4: State the solution<br />### The solution to the system of equations is the point where the two lines intersect, which is $(-1, 2)$.