D. X=3cm
Since the triangles are similar, just set up a proportion to solve for x.
4/8=x/6. Then just cross multiply and solve from there.
Answer:
C
Step-by-step explanation:
15/10=1.5 so 1.5 is the scale factor.
12x1.5=18. So the answer is C.
B. 5:10 because 15-5=10 which is the number of pencils with erasers and the 5 left are the amount of pencils which are missing an eraser
The acceptable first step in simplifying the expression
is (a) 
The expression is given as:

To change the form of the expression, we simply perform several arithmetic operations on it.
Start by multiplying the expression by 1/1

Express 1 /1 as (1 - sec x)/(1 - sec x)

Rewrite the above expression as follows:

Hence, the acceptable first step is (a)
Read more about trigonometry ratios at:
brainly.com/question/24888715