import tensorflow as tf

a = tf.constant(3.5)
b = tf.constant(4.5)
c = a * b

# this is what you are doing
print(c)
# out: Tensor("mul_3:0", shape=(), dtype=float32)

# this is what you want
with tf.Session() as sess:
    result = c.eval()
    # Or use sess.run:
    # result = sess.run(c)

    print(result)
    # out: 15.75

    print(type(result))
    # out: <class 'numpy.float32'>