The sum of twice a and 4sorry if this isnt much info. that's all what was written in the paper

The way you wrote it could have 2 meanings:

Sum of twice a and 4 could be:
2a+4 or 2(a+4) which will give different results.

In the first case:
2a+4
a= 4/2
a= 2
So the sum would be 2*2+4 = 4+4 = 8

In the second case:
2(a+4) = 2a + 2*4 = 2a + 8
a= 8/2
a=4

2(4+4) = 2*8 = 16

If you need an equation, it would be y=2x+8, y would be how long it grew, x being weeks.if you need how long he was asleep, it would be 4 weeks if he started with no beard, the equation would be x=8÷2if he did have a beard before hand, the equation would be 2w+x=8