Did it step by step , hope it helps !
For this answer is will be b
Scale factor is the ratio of two corresponding sides.
Here we have two triangles, where the preimage is the smaller triangle and the image is the larger triangle.
So scale factor =14/18 = 7/9
And to find the missing variable, we need to set the ratio.
7/9 = 28/x
Cross multiplying both sides
7x = 28*9
x = 36
It's 100 because 1000/10 = 1000