Answer:
21%
Step-by-step explanation:
for the first 5 months Nikki saved $350 so she saved 70 every month. for the next 4 months she saved 690-350=340, so 85 per month. The rate of increase should be (85-70)/70=.214 round it to the nearest tenth is .21, to find the percentage just multiply 0.21 by 100 you get 21%