The porter in Macbeth's castle provides
for this tragedy

The significance of the Porter within Macbeth is twofold. Primarily, the Porter functions as comic relief, lessening the tension in the audience after the murder of King Duncan. The Porter also serves a thematic function, indicating that the gates to Macbeth's home are synonymous with the gates of hell.

simplify brackets

8 - 2a - 7 = a + 40

simplify 8 - 2a - 7 to -2a + 1

-2a + 1 = a + 40

add 2a to both sides

1 = a + 40 + 2a

simplify a + 40 + 2a to 3a + 40

1 = 3a + 40

subtract 40 from both sides

1 - 40 = 3a

simplify 1 - 40 o -39

-39 = 3a

divide both sides by 3

-39/3 = a

simplify 39/3 to 13

-13 = a

switch sides

a = -13