Answer:
a = -15
Step-by-step explanation:
Let's rewrite the exercise in math language.
We have to subtract a-4 from 4a+16 to get -25, that is
4a+16 - (a-4) = -25
The minus sign that is just before the parenthesis changes all the signs inside it. Therefore, if we want to delete the parenthesis, we need to change the signs before.
4a + 16 - a + 4 = -25
Now we can associate the terms with an a between them and the terms without it from the left side of the equation.
3a + 20 = -25
Let's subtract 20 on both sides.
3a + 20 - 20 = -25 - 20
3a = -45
Finally, we divide by 3 on both sides
3a/3 = -45/3
a = -15
