A student solves the following problem:

Problem:
2(x-3) + 3x = 19
Step 1:
2x - 6 + 3x = 19
Step2:
(2x + 3x) -6 = 19
Step 3:
5х - 6 = 19
Step 4: 5x - 6 + 6 = 19 + 6
Step 5: 5x = 25
Step 6: x = 5
What property justifies going from step 3 to step 4?

The property that justifies going from step 3 to step 4 is the addition property of equality. This property allows the student to add the same number, 6, to both sides of the equation in order to isolate the variable, x.