3(2x+5)-7=2(4x-6) please solve equation

Can someone me and do the problem plz so i can understand it more better

Look at arnold's attempt to solve the equation for b: 3b = 12 b = 3 · 12 b = 36 describe the mistake that arnold made.

On saturday a souvenir shop had 125 customers. sixty four percent of the costumers paid with a credit card. how many costumers paid with cash?