I'll solve 11-14 since they are fairly simple problems once you get to understand them :)
Remember: what you do to one side of the equation, you do to the other.
To get everything on one side of the equation, you perform the opposite operation.
Say for example, 4x = 8. Since you are multiplying 4 * x, the opposite operation of multiplication is division, so in this case you would DIVIDE both sides by 4.
11) 15 = 6.5 + x
The opposite of addition, 6.5 + x, is subtraction, so subtract 6.5 from both sides.
15 - 6.5 = x
8.5 = x, which is the same as x = 8.5.
12) -3 + x = -17
The opposite of subtracting is addition, so add 3 to both sides.
x = -17 + 3
x = -14
13) 7x = -98
You have 7 * x, which is multiplication, and the opposite of multiplication is division, so divide both sides by 7.
x = -98/7
x = -14
14) x/-3 = -7
The opposite of division is multiplication, so multiply both sides by -3.
