3 pounds $0.90 how much will 10 pounds cost?

$\dfrac{\text{3 pounds}}{\text{0.90}}=\dfrac{\text{10 pounds}}{x}\\ \text{3x pounds} = \text{9 pounds}\\ 3x = 9\\ x = 3$

10 pounds will cost $3.

My weight is about 100 pounds and it would cost me about $30. LOL