Strategy 1: To transport 1/42 to the other side, take a reciprocal of it and becomes 42. To get the value x, this 42 is multiplied by 3/7. That is
x = 42*(3/7) = 126/7 = 18
Strategy 2: To cancel 1/42 beside x, you multiply by 42 on both sides.
[(1/42)*x]*42 = 42*(3/7)
x = 126/7
x = 18