Answer:

Step-by-step explanation:
The picture shows three isosceles tirangles with the same legs. The base of each triangle is 12 units, 5x-3 units and 17 units.
Since the angles at vertex of each isosceles triangles are 27°, 28° and 29°, then the lengths of the bases satisfy the double inequality
15<5x-3<17
Add 3 to this inequality
15+3<5x-3+3<17+3
18<5x<20
Divide it by 5:

Total number of marbles = 17
3 are black.
Not black = 17 - 3 = 14.
Probability of not black = Number not black / Total
= 14 / 17