I have difficulty( )(work)out the mach problem

(in) working
have difficulty (in) doing sth 做某事有困难
再问： 填什么？？
再答： 如果是一个空格，就填 working I have difficulty (working) out the mach problem 如果是两个空格，就一个填in，另一个填 working. I have difficulty ( in ) (working) out the mach problem