7/3 = 8c/5 .......multiply both sides by 5

=> 5(7/3) = 8c

=> 35/3 = 8c ....divide both sides by 8

=> 35/24 = c

check:

8(35/24)/5 = (35/3)/5 = 35/3 * 1/5 = 7/3....check!

so not sure why they'd ask you to check for extraneous solutions, there is only one solution i can see to this

extraneous solutions usually occur if you have to do something like square both sides to get the answer, otherwise, you should be good