Which of the following scenarios represents change to an ecosystem brought about by biotic factors?
a.
a wildfire caused by lightning striking a tree
b.
a flood caused by a severe storm
c.
a landslide caused by cattle overgrazing
d.
a volcano

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

b.have there own function.