Answer:
4.08 + 2 = 6.08 years
Step-by-step explanation:
we know that
Simple Interest(S.I.) = (P × R × T) ÷ 100
where, P = Principal = 750
R = Rate = 6%
T = unknown
⇒ S.I. = (750 × 6 × t)÷ 100
⇒ S.I. = 45t
Also, Amount = S.I + Principal
⇒ Amount = 750 + 45t
Now Formula for Compound Interest is:

where A = Amount
=1000
P = Principle
r = rate
t = total number of year
Here, P = 750 + 45t, r = 3.5% , and t = 2.
Putting all these values in above formula:

⇒ 
⇒ t = 4.08
Hence, total time required will be 2 + 4.08 = 6.08 years.
We are given equation g = 748u, where g is the total number of gallons of water used and u is the number of units.
We can see that the number of units of water being used by customers.
The number of units of water doesn't depend on the total number of gallons of water used.
Therefore, the number of units u is an independent variable.
The value of the total number of gallons is totally depends on the number of units used.
Therefore, the total number of gallons of water used g is a dependent variable.
So, we can conclude following statements:
1) g is the dependent variable.
2) u is the independent variable.
1.57, divide two times pi (3.14)