Which if the following is a requirement that units in a correct formula or equation must always satisfy?
a) each unit in the formula, expressed in si base units, must be the same.
b) all units must be units only of mass, length, or time.
c) the units on both sides of the equal sign, expressed in si base units, must be the same.
d) all masses must be in kilograms, all lengths in meters, and all times in seconds.

Asteel tube (k=50 w/mk) of inner and outer diameter di = 20mm and do=26mm, respectively, is used to transfer heat from hot gases flowing over the tube (h-hot = 200w/m2k) to cold water flowing through the tube (h-cold = 8000 w/m2k). what is the cold-side overall heat transfer coefficient uc? to enhance heat transfer 16 straight fins of rectangular profile are installed longitudinally along the outer surface of the tube. the fins are equally spaced around the circumference of the tube, each having a thickness of 2mm and a length of 15mm. what is the corresponding overall heat transfer coefficient uc? *solve for uc in both cases*