Jean camps beside a wide river and wonders how wide it is. She spots a large rock on the bank directly across from her.

θ45n160

https://www.google.com/search?q=Jean+camps+beside+a+wide+river+and+wonders+how+wide+it+is.+She+spots+a+large+rock+on+the+bank+directly+across+from+her.+She+then+walks+upstream+until+she+judges+that+the+angle+between+her+and+the+rock,+which+she+can+still+see+clearly,+is+now+at+an+angle+of+%CE%B8+%3D+45%C2%B0+downstream+(see+figure).+Jean+measures+her+stride+to+be+about+one+yard+long.+The+distance+back+to+her+camp+is+n+%3D+160+strides.+About+how+far+across,+both+in+yards+and+in+meters,+is+the+river%3F+yd+m&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjvxc_C9YTjAhUUuHEKHWQlBz8Q_AUIECgB&biw=1280&bih=648#imgrc=nglN18oRyKPQbM:

how would you go about setting up this problem?