Hello, Andy!
You didn't give us the rule for filling the boxes.
I will assume that it is an "additive" sequence . . .
Code:
* - - - *
| 42 |
* - + - * - + - *
| | |
* - + - * - + - * - + - *
| | | |
* - + - * - + - * - + - * - + - *
| 4 | T | 3 | 5 |
* - - - * - - - * - - - * - - - *
Assuming that each number is the sum of the two numbers below it,
. . we have this pyramid. Code:
* - - - *
| 42 |
* - + - * - + - *
| 2T+7 | T+11 |
* - + - * - + - * - + - *
| T+4 | T+3 | 8 |
* - + - * - + - * - + - * - + - *
| 4 | T | 3 | 5 |
* - - - * - - - * - - - * - - - *
The final "step" would be: .  + (T + 11) \:=\:42)
And we get: . 