A.

 I want to heat 950 GPH from 40-140^oF with 180^oF boiler water that I can take down to 160^oF. How much boiler water must I have available?

       950 x .01666 x ( 140-40) ₌ 1582.7 _{= 79 GPM of Boiled Water}
             180-160                    20

B.

 I have 30 GPM of 200^oF boiler water that I can take down to 160^oF. How many GPH of domestic water can I heat from 40-140^oF?

        30 x 60 x ( 200-160) ₌ 72000 _{= 720 GPH of Domestic Water}
             140-40                    100