Given an equation a+b+c+d=45 and relationships between the variables, the problem asks to compute the value of a+b+c-d. 1) Each variable is solved for in terms of a. 2) The values are plugged back into the original equation, yielding (9/2)a+9=45. 3) Solving this, the individual values are found to be a=8, b=12, c=5, d=20. 4) Plugging these values into a+b+c-d gives the final answer of 5.