70- sound wave travels through a pregnant woman's abdomen and is reflected from the fetal heart wall of her unborn baby. The heart wall is moving...

A 1.70- sound wave travels 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 beats per second are detected. The speed of sound in body tissue is 1490. Calculate the speed of the fetal heart wall at the instant this measurement is made.