If these two shapes are similar, what is the measure of the missing length b?

Answer:
B = 7mm
Step-by-step explanation:
This is probably an enlargement problem.
To solve this:
the blue triangle has all of it's measurements you need. Let's start with that.
6/36 =
We know that one side, the bottom side of the green triangle is 42mm.
6/36 = b/42
We could simplify 6/36 into 1/6
1/6 = b/42
AHA! the denominators are easy! 6 times 7 is equal to 42, so 1 times 7 should equal b!
1/6 = 7/42
Check:
6/36 = b/42
36b = 6*42
36b = 252
b = 252/36
b = 7
So yes! B is 7 mm. Pls mark me brainliest, as I never have a single brainliest.