For the integers a and b, the definition of "☆" is: a☆b=3a+4b, then what is the value of a that makes the equation (4☆3)☆a=172 true.
对整数a和b，规定"☆"的含义是：a☆b=3a+4b，则使等式(4☆3)☆a=172成立的a的值为多少．
<result>25</result>