Calculate.

a) 5 kg + 11 kg =
b) € 51 + € 6 =
c) 18 [[$ \dfrac{\text{m}}{\text{s}} - $]] 4 [[$\dfrac{\text{m}}{\text{s}}$]] + 1 [[$\dfrac{\text{m}}{\text{s}} $]] =
d) 8[[$x$]] + 9[[$x$]] =