notice, that, pure juice is 100% juice, dohhh, thus 100/100 = 1.00 50% is 50/100 or 0.50 in decimal format
so..... whatever those two quantities amount to, that is, the 50% and pure juice, or (4)(0.50) + (x)(1.00) they will equal the mixture desired 60% juice, or 0.60, namely (4+x)(0.60)
The system is almost right! The issue here is: when Sharon was adding the systems, she made a mistake. 15 + 9 = 24 not 26. From there, the rest of her steps are correct. Hope this helps!