Potassium ion enters the lumen of the by the process of active transport.
a. proximal tubule
b. renal corpuscle
c. loop of henle
d. distal tubule

a. proximal tubules because it is where it mostly enters the lumen and its process of transport

x = -6.5

explanation:

with this editor, you should be careful to put what you mean. 5/(2x - 7) = 3/(4x +14) is the way i will interpret it. cross multiply

5*(4x + 14) = 3*(2x - 7)       remove the brackets

20x + 70 = 6x - 21             add 21 to both sides

20x+ 70+21= 6x                 combine

20x + 91 = 6x                     subtract 20x

20x-20x+91=6x-20x           combine

91 = - 14x

x = - 91/14

x = - 6.5