[tex]a) \\ \\ xy = k | \div y \\ x = \frac{k}{y} [/tex]
[tex]b) \\ \\ 4x + 2y = 6 | - 2y \\ 4x = 6 - 2y | \div 4 \\ x = \frac{6 - 2y}{4} [/tex]
[tex]c) \\ \\ \frac{a + b}{x} = 3 | \times x \\ a + b = 3x | \div 3 \\ x = \frac{a + b}{3} [/tex]
