To solve this problem, we are going to set up a system of equations. In this example, we are going to use the variable w to represent the price of a watch and the variable c to represent the price of a calculator. Our two equations come right from the given information:
2w + 1c = 49
3w + 3c = 99
To solve this problem, we are going to manipulate the first equation so we can substitute it into the second equation.
2w + c = 49
c = 49 - 2w
Now, we must substitute this value for c into the second equation.
3w + 3(49 - 2w) = 99
Next we are going to distribute, simplify by combining like terms, and isolate the variable w.
3w + 147 - 6w = 99
-3w = -48
w = 16
Therefore, the cost of one watch is $16.
Hope this helps!