有一个美国数学题不懂,
Anobserverinalighthouseis70ftabovethewater.Hesightstwoboatsinthewaterdirectlyinfrontofhim.Theangleofdepressiontothenearestboatis400.Theangleofdepressiontotheotherboatis240.
Whatisthedistancebetweenthetwoboats?Roundtothenearestfoot.
A.107ft
B.84ft
C.98ft
D.91ft
标准答案是C,但是我觉得不对.我算的是73.80.求指导.