Shares of Halliburton Co. dropped sharply Monday after the company said it would buyBaker Hughes Inc. in a $34.6 billion stock-and-cash deal to combine two of the world’s largest oil-field services companies. Investors reacted negatively to the price Halliburton is paying for its smaller rival. Halliburton’s offer of $78.62 a share is 47% above where shares of Baker Hughes closed on Wednesday. The stock climbed Thursday when The Wall Street Journal reported that the companies were in talks. Halliburton shares fell 11% Monday to close at $49.23. Baker Hughes shares rose 8.9% to $65.23.