If you plot the points you can easily find the answer. (X,Y) The x-axis is the horizontal line and the y-axis is the vertical line.
Subtract to find the amount of tax paid:
1890 - 1800 = 90
Divide the amount of tax by the price of the computer:
90 / 1800 = 0.05
Multiply the decimal by 100:
0.05 x 100 = 5%
The tax rate is 5%
Plug any number in for x and find the resulting y, then if you need to graph place the coordinate points on the plane. For example if you set x=2 the equation becomes y=0.5(2). From here we can see 0.5(2)=1 and this is equal to 1 so in a data chart you would write under x the number 1 and under y the number 2.