Answer:
a. Let the variable be
for the fundraising activities and
as the revenue for foundation.
b. 
c. $43.2
d. $1416.67
Step-by-step explanation:
Given that:
The World Issues club donates 60% of the total of their fundraising activities.
Answer a.
Let us choose the variable
to represent the money earned during fundraising activities and
for the revenue generated for foundation.
Answer b.
Foundation will receive 60% of the total of the fundraising activities.
Equation to determine the money that will be received by foundation:

Answer c.
Given that x = $72, M = ?
Putting the value of x in the equation above:

Answer d.
Given that M = $850, x = ?
Putting the value of M in the equation above to find x:

So, the answers are:
a. Let the variable be
for the fundraising activities and
as the revenue for foundation.
b. 
c. $43.2
d. $1416.67