Help me with the following PERT problem please :(

A contractor requests the execution of a particular project. The activities and resource estimation are summarized in the following table. The figures are in monetary units and the duration in days.

Activity	Predecessor Activity	to	tm	tp
A	----	20	31	45
B	----	14	28	38
C	A	18	36	43
D	B	32	52	100
E	B	24	32	63
F	B	6	16	28
G	F,D	4	18	40
H	E,G	8	20	36
I	E,G	18	34	42
J	C,H	4	16	24

Determine: a) The probability of completing the project in 130 days. b) The probability of completing the project if you are granted 12 additional days. c) The number of additional days that must be requested if you want to have a 90% probability of completing it on time.