Emma took 35 pictures of flowers on a nature walk and an additional 3 pictures of each bird she saw. She took a total of 83 pictures. Which equation can be used to find the number of birds, x, that Emma saw on her walk?
a. 35x + 3x = 83
b. 35 + 3 = 83x
c. 35x + 3 = 83
d. 35 + 3x = 83