What is the least positive $x$ with $3x \equiv 4 \pmod{7}$?

Explanation

1. 01

   Try $x = 1, 2, \dots, 6$: $3x$ leaves 3, 6, 2, 5, 1, 4 on division by 7.

2. 02

   $x = 6$ gives $18 = 7 \times 2 + 4$.