To solve the equation, we need to isolate the variable "a" on one side of the equation. Let's solve each equation separately:

1) a*5 - 129 = 6

First, let's add 129 to both sides of the equation to get rid of the constant term on the left side:

a*5 - 129 + 129 = 6 + 129

This simplifies to:

a*5 = 135

Next, divide both sides of the equation by 5 to solve for "a":

(a*5)/5 = 135/5

This simplifies to:

a = 27

So the solution for the first equation is a = 27.

2) a:5 + 158 = 4

First, let's subtract 158 from both sides of the equation to get rid of the constant term on the right side:

a:5 + 158 - 158 = 4 - 158

This simplifies to:

a:5 = -154

Next, multiply both sides of the equation by 5 to solve for "a":

(a:5)*5 = -154*5

This simplifies to:

a = -770

So the solution for the second equation is a = -770.

Therefore, the solutions to the given equations are a = 27 and a = -770.