1) 2x + 9 = 13 - x;

2x + x = 13 - 9;

3x = 4;

x = 1 1/3;

2) 0.5a + 11 = 4 - 3a;

0.5a + 3a = 4 - 11;

3.5a = -7;

a = -2.