3/8 (5+6x)+3> 21

3/8 (5 + 6x) + 3 > 21

Multiply through by 8 (multiply each term by 8) to eliminate fractions.

8[3/8 (5 + 6x)] + 8[3] > 8[21]
3(5 + 6x) + 24 > 168

distribute the 3
15 + 18x + 24 > 168

combine like terms
18x + 39 > 168

isolate the variable by subtracting 39 from both sides

18x > 129

finish by dividing both sides by 18.