To find this, you can simply multiple both the numerator and denominator (top and bottom) by any number as long as it's the same number for both top and bottom. In this case, we used 2 as the number, and multipled it to the top and bottom of 2/3, to get 4/6.
To answer the question above, we let s be the cost of a shirt and h be the cost of each hat such that the equations that would best represent the given are: 10s + 20h = 490 20s + 30h = 860 The system of equations is the answer to the first question and the values of s and h are $25 and $12, respectively.