There are several stamps with denominations of 0.5 yuan, 0.8 yuan and 1.2 yuan respectively, the face value is 60 yuan in total, and the number of stamps with a denomination of 0.8 yuan is 4 times the number of stamps with a denomination of 0.5 yuan. Then, the denomination of 1.2 yuan How many stamps are there?
有若干张面值分别为0.5元、0.8元和1.2元的邮票，面值共60元，其中面值为0.8元的邮票张数是面值为0.5元邮票张数的4倍，那么，面值为1.2元的邮票有多少张．
<result>13</result>