"These units are not compatible"

[JLand0299]

I always run into this problem. I don't know why

[Werner_E]

Can't you see that every of your three summands has different units? You simply can't add quantities of different dimensions!

Furthermore you are missing a multiplication sign between C.l and the parenthesis. Without that multiplication sign Prime assumes a function C.l with T.p-T-m as argument.

[JLand0299]

I was just told by my instructor that this particular problem can not be done in MathCad. Due to the fact that the actual unit for C_l and C_s needs to be Btu/ (lbm*F) or something like that. He just told me to add values without units for just a numerical answer. I do see where I need to add the multiplication to the formula. 

[Werner_E · Accepted solution]

---

@JLand0299 wrote:

I was just told by my instructor that this particular problem can not be done in MathCad. Due to the fact that the actual unit for C_l and C_s needs to be Btu/ (lbm*F) or something like that. He just told me to add values without units for just a numerical answer. I do see where I need to add the multiplication to the formula. 

---

I am pretty sure that this problem CAN be done in Mathcad and even in Prime. You just have to use Delta °F instead of just °F. Temperature units are a bit tricky - if you want to be on the simple and safe side you may consider using K throughout.

But there still is a unit mismatch in the first summand - there's missing lb or lbm in the denominator.

I added it the bold way in the following screenshot but you'll have to check the formula or the units assigned:

[JLand0299]

Thank you sir for all your help. I appreciate your knowledge and I will pass along what I had learned.