Answer:
Identity property of multiplication
Step-by-step explanation:
From step 5:

Here, to solve for x so that the variable x stands alone, Alberto uses the identity property of multiplication, which justifies what he has in step 6.
Step 6:

According to the identity property of multiplication, any value you multiply by 1 gives you that same value.
Therefore, 1x = 1 × x = x.
The variable x multiplied by 1 will give you x.
I thinks its B
p.s. spread le cheese ⌂
The answer is B.
(the equation to solve this with is: a^2 + b^2 = c^2)
Treat it just like and equation at first. Multiply the 10 on both sides to get rid of it, leaving you with 50
x. Then on the number line, since there is a line under it, you would make a filled in circle and an arrow pointing towards 51 and beyond