It takes 3.78 J of work to stretch a Hooke’s-law spring 14.2 cm from its unstressed length. How much the extra work is required to stretch it an additional 11.2 cm? Answer in units of J.
Take a look at this:
https://www.jiskha.com/questions/1820255/it-takes-3-78-j-of-work-to-stretch-a-hookes-law-spring-14-2-cm-from-its-unstressed
It's a direct proportion: J/cm = J/cm
3.78 J / 14.2 cm = (3.78 + x) J / (14.2 + 11.2) cm
3.78 J / 14.2 cm = (3.78 + x) J / 25.4 cm
Cross-multiply: 3.78 J · 25.4 cm = 14.2 cm · (3.78 + x)
Solving for x: x = 2.98
+11 
