Solution for an=19-7(n-1) equation: 
 
Simplifying 
an = 19 + -7(n + -1) 
 
Reorder the terms: 
an = 19 + -7(-1 + n) 
an = 19 + (-1 * -7 + n * -7) 
an = 19 + (7 + -7n) 
 
Combine like terms: 19 + 7 = 26 
an = 26 + -7n 
 
Solving 
an = 26 + -7n 
 
Solving for variable 'a'. 
 
Move all terms containing a to the left, all other terms to the right. 
 
Divide each side by 'n'. 
a = 26n-1 + -7 
 
Simplifying 
a = 26n-1 + -7 
 
Reorder the terms: 
a = -7 + 26n-1