Answer
Please see the work below.
Work Step by Step
We know that energy-efficient:
$(0.225KW)(0.11t hour)(\$ 0.095 )=0.00235125t$
standard:
$(0.425KW)(0.20t\space hour)(\$ 0.095)=0.008075t$
Now the difference is
$0.00235125t-0.008075t=1150-850$
We can solve it for time as:
$t=\frac{1150-850}{0.008075-0.00235125}=52413h=6.0yr$
