Solve equation for X

The hawaiian alphabet has 12 letters. how many permutations are posible for each number of letters?

Which of these equations, when solved, gives a different value of x than the other three? a9.1 = -0.2x + 10 b10 = 9.1 + 0.2x c10 – 0.2x = 9.1 d9.1 – 10 = 0.2x

Which letters from the table represent like terms? a and b b and c a and d b and d