To solve these equations, we need to isolate the variable (x) on one side of the equation.

x + 3/7 = 2/5 + 3/1

First, we need to combine the fractions on the right side of the equation:

x + 3/7 = 13/5

Next, we need to isolate x by subtracting 3/7 from both sides:

x = 13/5 - 3/7

Now we need to find a common denominator for the fractions:

x = (91/35) - (15/35)

x = 76/35

2/3 - x = 8?21

First, we need to simplify the right side of the equation:

8?21 = 8/21

Next, we need to isolate x by subtracting 2/3 from both sides:

-x = 8/21 - 2/3

Now we need to find a common denominator for the fractions:

-x = (8/21) - (14/21)

-x = -6/21

-x = -2/7

Finally, we need to solve for x by multiplying both sides by -1:

x = 2/7

19/20 - x = 8/5- 3/4

First, we need to simplify the right side of the equation:

8/5 - 3/4 = 32/20 - 15/20

8/5 - 3/4 = 17/20

Next, we need to isolate x by subtracting 19/20 from both sides:

-x = 17/20 - 19/20

-x = -2/20

-x = -1/10

Finally, we need to solve for x by multiplying both sides by -1:

x = 1/10