math

To solve  -4  <  5x + 12  <  3  get the x-term alone in the center by removing both the 12 and the 5.

To remove the 12, subtract 12 from all three parts:  -4 - 12  <  5x + 12 - 12  <  3 - 12

     --->     -16  <  5x  <  -9

To remove the 5, all three parts by 5:     -16 / 5  <  5x / 5  <  -9 / 5

     --->     -3.2  <  x  <  -1.8