Jackie wants to keep her total work time under 20 hours, so we can set up a rough inequality right away:
(work time in hours) < 20
Now, it's going to take here 1/2 = 0.5 hours to finish each necklace, an 1 hour to finish each bracelet, so if she's making x necklaces, it'll take her 0.5x hours to make all of them, and if she's making y bracelets, it'll take her 1y = y hours to finish those. Putting the two together, it'll take her 0.5x + y hours altogether to make the necklaces and bracelets. Putting that together with our first inequality, we get the final inequality
0.5x + y < 20
