The number z and −1.9 are additive inverses. drag and drop −1.9 and z to their correct positions on the number line. drag and drop the label “sum” to the sum of −1.9 and z

Additive inverses are numbers that add up to zero, such as 1 and -1. 
Z is the additive inverse of -1/9, so z is 1.9.
1.9 + -1.9 =0.

Drag the -1.9 icon to just one mark to the right of -2 on the number line, since each dash equals 0.1.
Drag z to just one mark to the left of 2 on the number line.
The sum will be zero, so drag the sum icon to 0 on the number line. 

The last answer choice

Answer is negative 2