Well, I saw my teacher solving the test herself, and then grading papers off of her paper that she solved. My teacher made the answer key for the tests.
You would use the formula for the specific term you wish to find;
The formula is:

a = starting value of the sequence
d = the common difference (i.e. the difference between any two consecutive terms of the sequence)
n = the value corresponding to the position of the desired term in the sequence (i.e. 1 is the first term, 2 is the second, etc.)
Un = the actual vaue of the the term
For example, if we have the arithmetic sequence:
2, 6, 10, 14, ...
And let's say we want to find the 62nd term;
Then:
a = 2
d = 4
(i.e. 6 - 2 = 4, 10 - 6 = 4, 14 - 10 = 4;
You should always get the same number no matter which two terms you find the difference between so long as they are both
consecutive [next to each other], otherwise you are not dealing with an arithmetic sequence)
n = 62
And so:
<span>Melvina's age is = x, Bettina's age is = 3x
the equation is
x + 20 = 3x - 20
subtract 3x from both sides
-(3x) + x +20 = 3x - 20 - (3x)
-2x + 20 = -20
subtract 20 from both sides
-2x + 20 - (20) = -20 - (20)
-2x = - 40
divide both sides by -2
(-2x)/-2 = (-40)/-2
x = 20
Melvinas age is 20 and Bettinas age is 60</span>
A system of linear equations will have no solution when the two lines making up the equation are parallel. Here, a system having x + y = 2 will have no solution if the second equation is x + y = a. where a is any real number.