How do you know the correct order on which to evaluate algebraic expressions

Compare these two waves: the blue and orange waves have the same pitch, but the blue wave is louder. the blue and orange waves have the same volume, but the blue wave has a higher pitch. the orange wave has a higher pitch, but the blue wave is louder. the blue wave has a higher pitch, but the orange wave is louder.

For each proportion find the unknown number x 1/5/8=×/15

Find the commission on a $590.00 sale if the commission is 15%.