Resource is() A the waste from industries.
B
a usable stock or supply
С
a forceful river.

A forceful river.

Explanation:

Resources are the means necessary to carry out a certain action. A resource can be a tangible or intangible good that can use for certain economic purposes. Rijeka can be an excellent resource that can be used, for example, to irrigate farms or build a hydroelectric power plant. Production equipment, natural and mineral resources, soil, and other raw materials are the most common 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