Answer:
We know that:
She needs 9/10 grams of flour for the cake (this quantity does not make a lot of sense, maybe is written incorrectly, but is the only info we have, so let's solve the problem with this)
She only has 1/3 of the amount she needs.
How much flour does she have?
Well, she needs 9/10 grams, and she has one-third of that.
Then she has (1/3) times (9/10) grams, this is:
F = (1/3)*(9/10) grams
F = (1*9)/(3*10) grams
F = 9/30 grams
That is the amount of flour that she has.