9 + 9 + 3 = 21 (Small hand on clocks)
10 + 10 + 10 = 30 (The value of the calculator is the sum of the digits in the display (1+2+3+4)
15 + 15 - 15 = 15 ( 5 Rays * 3 rings on the bulb = 15)
9 (time) + 9 (sum of digits) * ((4 rays * 3 rings)*3 (total bulbs))
9 + (9 * ((12)3))
9 + (9 *36)
9 + 324 = 333

OF COURSE WE HAVE TO MAKE ASSUMPTIONS AND TECHNICALLY THIS SHOULD BE WRITTEN AS UNSOLVABLE:
a + a + b =21
c + c + c = 30
d + d - d = 15
a + (e * (3f)) = ?
Unsolvable.

Revised based on difference in height of bulb in the final grouping
9 + 9 + 3 = 21 (Small hand on clocks)
10 + 10 + 10 = 30 (The value of the calculator is the sum of the digits in the display (1+2+3+4)
15 + 15 - 15 = 15 ( 5 Rays * 3 rings on the bulb = 15)
9 (time) + 9 (sum of digits) * ((4 rays * 3 rings)+2(4 rays * 4 rings))
9 + (9 * ((12)+2(16)))
9 + (9 *44)
9 + 324 = 405

a + a + b =21
c + c + c = 30
d + d - d = 15
a + (e * (f+2g)) = ?

Unsolvable.