The First-Order Decomposition of Phosphene to Phosphorus and Hydrogen 4PH₃(g)

The first-order decomposition of phosphene to phosphorus and hydrogen 4PH₃(g)  P₄(g) + 6H₂(g)
Has a half-life of 35.0 s at 680°C. Starting with 520 mmHg of pure phosphene in an 8.00-L flask at 680°C, how long will it take for the total pressure in the flask to rise to 1.000 atm?

A) 628 s
B) 33.4 s
C) 51.2 s
D) 111 s
E) 48.3 s