Normally when there is similar terms and when you have to figure out if it is factorable or prime you must first begin factoring it and if it does not work it is prime.
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Answer: His total rental cost will be $164.75.
Step-by-step explanation:
Since we have given that
Cost of per day = $30
Cost of per mile after the first 100 miles = $0.65
According to question, he was travelling 215 miles in 3 days.
So, it becomes,

Hence, his total rental cost will be $164.75.
Simplifying
(0.75x + 6) + -1(2.5x + -1.9) = 0
Reorder the terms:
(6 + 0.75x) + -1(2.5x + -1.9) = 0
Remove parenthesis around (6 + 0.75x)
6 + 0.75x + -1(2.5x + -1.9) = 0
Reorder the terms:
6 + 0.75x + -1(-1.9 + 2.5x) = 0
6 + 0.75x + (-1.9 * -1 + 2.5x * -1) = 0
6 + 0.75x + (1.9 + -2.5x) = 0
Reorder the terms:
6 + 1.9 + 0.75x + -2.5x = 0
Combine like terms: 6 + 1.9 = 7.9
7.9 + 0.75x + -2.5x = 0
Combine like terms: 0.75x + -2.5x = -1.75x
7.9 + -1.75x = 0
Solving
7.9 + -1.75x = 0
Solving for variable 'x'.
Move all terms containing x to the left, all other terms to the right.
Add '-7.9' to each side of the equation.
7.9 + -7.9 + -1.75x = 0 + -7.9
Combine like terms: 7.9 + -7.9 = 0.0
0.0 + -1.75x = 0 + -7.9
-1.75x = 0 + -7.9
Combine like terms: 0 + -7.9 = -7.9
-1.75x = -7.9
Divide each side by '-1.75'.
x = 4.514285714
Simplifying
x = 4.514285714