How do you do a math question like 8-(4-n)=10 and 6y-2(y+1)=18?

Get rid of the brackets. Then isolate the unknown. Solve.

a)
8 - (4 - n) = 10
8 - 4 + n = 10
n = 10 - 8 + 4
n = 6
Check:
8 - (4 - 6) = 8 - (-2) = 8 + 2 = 10

b)
6y - 2(y + 1) = 18
6y - 2y - 2 = 18
4y - 2 = 18
4y = 20
y = 20 / 4 = 5
Check:
6 * 5 - 2 * (5 + 1) = 18
30 - 12 = 18