Letting C be the cost of a chair and T be the cost of a table, we have 12C+ 15T= 58968. That is NOT enough to solve for either C or T. We could, for example, divide by 3 to get 4C+ 5T= 19656. But that is not "4C+ 5T". If wewereable to determine 4C+ 7T= A, we could get, by subtracting, 2T= 19656- A and so solve for T and, of course, then, solve for C. Since, in fact, there exist an infinite number of values of T and C that satisfy 12C+ 15T= 58968, there are an infinite number of values of A in 4C+ 7T= A.