Answer:
4 pounds of mud
Step-by-step explanation:
Let the mud be added as
pounds.
Given:
Cost of 1 pound of mud = $ 1.50
∴ Cost of
pounds of mud = 
Cost of 1 pound of pitch black = $ 2
∴ Cost of 6 pounds of pitch black = 
Amount of Texas T made =
pounds.
Cost of 1 pound of Texas T = $ 1.80
∴ Cost of
pounds of Texas T = 
Now, cost of Texas T will be equal to the sum of cost of mud and pitch black. This gives,

Therefore, he used 4 pounds of mud coffee.