Help me with these three quesions for brainiest:)

See below.

Step-by-step explanation:

1) Two equations are equivalent if they have the same solutions.

2) As long as two expressions and are equal, so , adding the same value for both sides still makes the equation true, so

is true.

3) As long as two expressions and are equal, so , subtracting the same value for both sides still makes the equation true, so

is true.

341

step-by-step explanation:

all you have to do is 9x31 (which equals 279) and then 20x31 (which equals 620). then you have to subtract. 620-279=341.