zack has a bag of cherries he gives away 18 cherries to Tim and 18 cherries to janet. now he has 25 cherries . how many cherries did zack have at the start?

If Zack had 25 cherries after giving 18 cherries each to Tim and Janet, he gave away a total of 18 + 18 = <<18+18=36>>36 cherries.

If Zack had 25 cherries left after giving away 36 cherries, then Zack had 36 + 25 = <<36+25=61>>61 cherries at the start. Answer: \boxed{61}.