A sound wave travels at a frequency 1.95 Mhz through a pregnant woman's abdomen and is reflected from the fetal heart wall of her unborn baby. The heart wall is moving toward the sound receiver as the heart beats. The reflected sound is then mixed with the transmitted sound, and 90.0 beats per second are detected. The speed of sound in body tissue is 1500 m/s. Here is what I came up with so far. (freq of beats) = [(speed of sound in body tissue)+(speed of listener, the reciever)]/[(speed of sound in body tissue)+(speed of source, the heart wall)] * (given freq sound wave) - (given freq sound wave) so 90 = (1500 +0)/(1500 + speed of heart wall) *1.95x10^6 - 1.95x10^6 and I end up with a negative number -.06922 What am Im doing wrong?? Thank you for your help. I also tried just entering .06922 however the answer was still wrong.