3a - (a - 7) = 15, How do you find out what a is?

Ben's the closest.

3a - (a - 7) = 15

Forget subtraction. There is, in reality, no such thing. You';ll find that out later in your math career...

3a - (a - 7) really means
3a + (-1)[a + (-7)]3a + (-1)(a - 7) and (a-7) really means
(a + [-7]). This may seem a little awkward, but it's harder to lose track of the signs this way.

So
3a - (a - 7) really reads

3a + (-1)[a + (-7)]

NOW distribute as Ben suggests
3a + (-1)[a + (-7)] =
3a + [(-1)(a) + (-1)(-7)] =
3a + [(-a) + 7] =
[3a + (-a)] + 7 because of the associative property of addition.
= 2a + 7 = 15... and you can probably take if from here.

2a + 7 = 15
2a = 8
a = 4

3a - (a - 7) = 15
3a - a + 7 = 15
2a + 7 = 15
2a = 15 - 7
2a = 8
a = 8/2
a = 4

LOL..............!!!!!!!!!

multiply the elements in the brackets with the sign wich is b4 the brackets

i.e.,3a-a+7=15

Then , bring only variables at one side
3a-a = 15-7
2a = 8
a = 4

I think u r clear now!!!!!!!!!!!!!!!!!!

3a - (a-7) = 15

2a+7 = 15

2a= 8
a=4.

This is very simple just concentrate on yourself have faith in yourself. Take care while doing the solving part just follow BODMAS or BEDMAS. Good luck

3a - (a - 7) = 15

Distribute:

3a - a + 7 = 15

Combine like terms:

2a + 7 = 15

Subtract 7 from each side:

2a + 7 - 7 = 15 - 7

Combine like terms:

2a = 8

Divide each side by 2:

(2a)/2 = 8/2

Simplify:

a = 4

First. you simplify 3a - (a - 7) = 15
3a - a + 7 = 15
2a + 7 = 15

Then you solve for a:
2a = 15 - 7
2a = 8
a = 4

just distribute the sign to the elements between the parantheses so u get:
3a-a+7=15
now move the elements with variable "a" to one side and the numbers to the other and u get:
2a=15-7
2a=8
a=4

First get rid of the brackets. In this case because there is a negative before the brackets multiply everything inside them by negative one, then solve as a normal equation.

3a - (a-7) = 15
3a - a +7 = 15
2a + 7 = 15
a = 4