The sum of all possible values of a, for which the 4-digit number 547a is divisible by 3, is

• 7

• 15

• 10

• 13

A common factor of ${\mathrm{x}}^4 - 256, {\mathrm{x}}^3 - 4{\mathrm{x}}^2 +\hspace{0.17em}3\mathrm{x} - 12 \mathrm{and} {\mathrm{x}}^2 - 7\mathrm{x} + 12 \mathrm{is}$

• x + 4

• x - 3

• x - 4

• x + 3