by selling an item at $20.70, a trader makes a profit of 15%. at what price should he sell the item so as to make a profit of 35%

$24.30

If something is sold at a profit of 15%, we write that percentage as 0.15. When we’ve added that to the whole amount we got the percentage from, we wrote that as 1.15 (115%)

If x is the cost of the item
1.15x = 20.70
Divide both sides by 1.15
x = 18

If the item originally cost 18, and we want a 35% profit, that’s 135% of the cost, or 1.35 as a decimal
18 x 1.35 = $24.30

Ac equals 35 cm long