10 x 25 = 250, well 20 x 25 is just double that, its 10 doubled x 25 so he probably just added it up. repeated addition really helps with times tables.
I would say F cause a triangle sides add up to 180
Answer:
x = -1
Step-by-step explanation:

Add 4x to each side of the equation


Subtract ⅚ from each side





Divide both sides by -5



What are you trying to find ?