Do you think there was any way the native populations could have expelled Europeans from the Americas?

No, I don't think so. When Europeans first arrived in America, they were already using metals and gunpowder, while the native population of America was still using stone tools and had just started experimenting with bronze. Moreover, Europeans bought many pathogens with them from which they themselves were immune, but the native population was not. The flu virus alone is said to have wiped most of the population. Europeans could not have been defeated because they had better technologies and resources.

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