6th grade math I mark as brainliest

 21 units

Step-by-step explanation: Since the y-coordinates are the same, you need to find only the difference in the x-values.

Since one is positive and one is negative, (on different sides of the y-axis) you add the distances of each coordinate from there.

Or, remember that finding the difference between two numbers is a subtraction equation, and subtracting a negative is the same as adding a positive.

15 -(-6) = x

15 + 6 = x

21 = x

the expression (1.26)2t reveals the approximate rate of increases in the number of plants semiannually.

hope this : )