3 | = | 1 |

| |

45 | 5x |

Cross multiply:
3 * 5x = 45 * 1
Simplifying
3 * 5x = 45 * 1
Multiply 3 * 5
15x = 45 * 1
Multiply 45 * 1
15x = 45
Solving
15x = 45
Solving for variable 'x'.
Move all terms containing x to the left, all other terms to the right.
Divide each side by '15'.
x = 3
Simplifying
x = 3