PLS HELP ASAP

Heat from the sun reaches earth to a. radiation b. convection c. conduction

Your target variable is δf, the magnitude of the difference in frequency between the waves emitted from the sonar device and the waves received by the device after reflecting off the whale. write an expression for δf in terms of the relevant frequencies using the subscript notation introduced above.

If anyone who can me with this hw? i would really appreciate it