water is following at a rate of $3$ lb$/$s through a $0\mathrm{.}35$ in diameter straight tube. The water has an inlet tempurature of $115$ F and it is desired to heat the water to a mean temperature of $175$ F at the exit of the tube. the surface of the tube is maintained at $300$ F$.$ Determine the required length $($ft$)$ of the tube. do not use Si units please.