Target Costing

Hi Sir Sorry I am having a mind block moment. Question- Product cost $10 target profit= 25% on cost current cost=8.40 whats the target cost gap? Target costing= Market price- desired profit margin $10-(25%*8.40)= 10-2.1= 7.90 8.40-7.90= =0.50 but the answer is wrong? The solution goes on to calculate the target profit as 25% on cost is the same as 20% on price. I am confused by this statement. how is 25% on cost the same as 20% on price? thanks