The post office is at the corner of First Street and Main Street, which forms a right angle. First Street intersects with Oak Street to the north, and Main Street intersects with Oak Street to the east. The intersection of First Street and Oak Street forms an x° angle, and tan x° = seven fifths. Car A drives on Main Street for 21 miles to arrive at Oak Street. How far will car B have to travel on First Street to get to Oak Street? A 15 miles B 20 miles C 25.4 miles D 29.4 miles