Answer: The number would be 18
Step-by-step explanation:
18/2=9 9-3=6 6*3=18
We see on the picture that :
When we go down one row, we add one horizontal and two diagonal cards.
In the first row we have 2 cards
In the second 2+3=5 cards
In the third 5+3=8 cards
etc.
General formula : in the n-th row from the top, we have
Midpoint Formula: (

,

)
Midpoint = (

,

)
Midpoint = (

,

)
Midpoint = (

, -4)
So, the midpoint of the endpoints (-4,-3) and (7,-5) is (

, -4).
Have a nice day! ♪