A: 333

The clocks in the first row represent 9 + 9 + 3

The calculators in the second row are each 10 (also 1234 added together is 10)

Each lightbulb in the third row is 15 (15 + 15 – 15) = 15.

Which means each ray above the lightbulb =3

So in the last row:

9 + 9 x (12 + 12 + 12)

9 + 9(36)

9 + 324

333

10/31/20 update from Colin Porteus — thanks for your sharp eyes!!

Hello Robin, can you check the last row on this one please? I get 9 + 9 x (12 + 16+ 16)?? The bottom two globes have 4 threads each x the 4 light marks makes them 16 each?? So consequently I get a result of 405.

Thank you