Let x be the number of hours spent tutoring English. Then, the number of hours spent tutoring mathematics would be 40 - x (since there are 40 students in total and no student took both types of tutoring).
The weekly income received by the center from English tutoring is the product of the hourly rate and the number of hours spent tutoring English, which is 18x.
Similarly, the weekly income received by the center from mathematics tutoring is the product of the hourly rate and the number of hours spent tutoring mathematics, which is 20(40 - x).
We can present these results in the following number-value table:
English tutoring Mathematics tutoring
Rate $18 per hour $20 per hour
Hours x 40 - x
Income $18x $20(40 - x)