Solve using substitution. 7x+8y=-9 5x-4y=13 d square

To solve the system of equations using substitution, we can solve one equation for one variable and then substitute that expression into the other equation.

Let's solve the first equation for $$x$$ :
$$7x + 8y = -9$$
$$7x = -9 - 8y$$
$$x = \frac{-9 - 8y}{7}$$

Now, substitute this expression for $$x$$ into the second equation:
$$5x - 4y = 13$$
$$5\left(\frac{-9 - 8y}{7}\right) - 4y = 13$$
$$\frac{-45 - 40y}{7} - 4y = 13$$
$$-45 - 40y - 28y = 91$$
$$-68y = 136$$
$$y = -2$$

Now that we have the value of $$y$$ , we can substitute it back into the expression for $$x$$ :
$$x = \frac{-9 - 8(-2)}{7}$$
$$x = \frac{-9 + 16}{7}$$
$$x = \frac{7}{7}$$
$$x = 1$$

Therefore, the solution to the system of equations is $$x = 1$$ and $$y = -2$$ .