What type of combat characterized wwi?

Trench Warfare. Which often consisted of long dug out trenches, and opposing sides "going over the top" in an attempt to overwhelm the other forces. This led to the phrase "No mans land", the space in between trenches where men would be killed almost immediately if they were made to go. Other characteristics of WW1 combat would be the massive technological advancements that came with the industrial revolution, and weaponized   chemicals making a debut to the world through WW1.

mass production/ assembly line production

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