A certain airline's fleet consisted of 90 type A planes at the beginning of 1980. At the end of each year, starting with 1980, the airline retired 3 of the TYPE A planes and acquired 4 new type B plans. How many years did it take before the number of type A planes left in the airline's fleet was less than 50 percent of the fleet?  Choose the most appropriate option.
A) 11 B) 12 C) 13 D) 14 E) 15
Let x be the number of years.   4x &gt; 90 - 3x   7x &gt; 90   x &gt; 12 + 6/7   The answer is 13.
<result>C</result>
A certain airline's fleet consisted of 90 type A planes at the beginning of 1980. At the end of each year, starting with 1980, the airline retired 3 of the TYPE A planes and acquired 4 new type B plans. How many years did it take before the number of type A planes left in the airline's fleet was less than 50 percent of the fleet?