A negative charge of -0.550 C exerts an upward 0.900-N force on an unknown charge that is located 0.500 m directly below the first charge. Part A What is the value of the unknown charge (magnitude and sign)? Express your answer with the appropriate units. 9= 30.0 Part B C Value Units input for part A What is the magnitude of the force that the unknown charge exerts on the -0.550 C charge? Express your answer with the appropriate units. Units