Applying the first law of thermodynamics, we know that the heat transferred is equivalent to the work done and the internal energy of the bodies.
In mathematical terms this can be expressed as
[tex]Q = W+\Delta U[/tex]
According to the statement, the work is carried out on the substance, therefore, the work will be negative (by convention)
[tex]Q = -350+50lbm(150-89)Btu/lbm[/tex]
[tex]Q = 2700Btu[/tex]
Therefore 2700Btu were added as heat to the substance.
The value per unit of mass would be
[tex]\dot{Q} = \frac{2700}{50}[/tex]
[tex]\dot{Q} = 54Btu/lbm[/tex]
Therefore it was added around to 54Btu/lbm
