Simultaneous Equations Solver

How to design a program that can solve mixed simultaneous equations, that is , one linear equation and one quadratic equation. Here is the program:

Private Sub Command1_Click()
Dim a, b, c, d, m, n As Integer
Dim x1, x2, y1, y2 As Double
a = Val(Txt_a.Text)
b = Val(Txt_b.Text)
m = Val(Txt_m.Text)
c = Val(Txt_c.Text)
d = Val(Txt_d.Text)
n = Val(Txt_n.Text)
x1 = (m * a * d + Sqr(m ^ 2 * a ^ 2 * d ^ 2 - (b ^ 2 * c + a ^ 2 * d) * (d * m ^ 2 - b ^ 2 * n))) / (b ^ 2 * c + a ^ 2 * d)
x2 = (m * a * d - Sqr(m ^ 2 * a ^ 2 * d ^ 2 - (b ^ 2 * c + a ^ 2 * d) * (d * m ^ 2 - b ^ 2 * n))) / (b ^ 2 * c + a ^ 2 * d)
y1 = (m - a * x1) / b
y2 = (m - a * x2) / b
Lbl_x1.Caption = Round(x1, 2)
Lbl_y1.Caption = Round(y1, 2)
Lbl_x2.Caption = Round(x2, 2)
Lbl_y2.Caption = Round(y2, 2)
End Sub
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Explanation:
Mixed simultaneous equations take the following forms:
ax+by=m
cx²+dy²=n
Simultaneous equations can normally be solved by the substitution or elimination methods. In this program, I employed the substitution method. So, I obtained the following formulae:
x1 = (m a d + Sqr(m ² a ² d ² - (b ² c + a ² d) (d m ² - b ² n))) / (b ² c + a ² d)
x2 = (m a d +-Sqr(m ² a ² d ² - (b ² c + a ² d) (d m ² - b ² n))) / (b ² c + a ² d)
y1 = (m - a x1) / b
y2 = (m - a x2) / b

To limit the answers to two decimal places, I used the round function.