I am not certain of what you wrote for the function but will assume that is likely exponential function or quadratic function.
First, (quadratic function) To solve this, you must know the quadratic formula. The x-intercept is value(s) that has the output value(y) of 0.
If the vertex of the quadratic function of (0,0), there is only one x-intercept. The number and value of the x-intercept depends on the slope and vertical displacement.
Second, (exponential function) note that there is no x-intercept. For instance, if a is 2, is there such value y that 2^y is 0? The smallest exponential value that is an integer is 1. Even broadening the limit to rational numbers, no such exponential value can have the result of 0. Therefore, in the basic form of exponential function, there is no x-intercept.
Let 
denote the <em>k</em>th term of the sequence. Then
where <em>d</em> is the common difference between consecutive terms in the sequence and <em>a</em>₁ is the first term.
The sum of the first <em>n</em> terms is
From the formula for , we get
So we have 
, and 
so that 
.
Then the <em>n</em>th term in the sequence is
$54.80 is the correct answer
