Answer:
7) a= 20
8) m= 5
9)n = 5
10) b = 8
Explanation:
7) 18+2=-2+2+a
>> 20 = a >> a = 20
18 + 2 = 20 so that isolates the variable leaving a = 20
8) -7+12 = m -12+12
>>> 5 = m >> m = 5
-7 + 12 = 5 so that again isolates the variable leaving m = 5
9) -8(7 + 7n) = -336
>> -56+56 + -56n = -336+56
>>> -56n/-56 = -280/-56
>>>> n = 5
use distributive property, cancel out necessary numbers, isolate the variable. leaving n = 5.
10) -140 = -7(-4 + 3b)
>> -140 = 28 - 21b >> -140-28 = -21b +28-28 ( flipped the numbers)
>>> -168/-21 = -21b /-21
>>>> 8 = b >> b =8
Hope it helps!