75% of what number is 12

Lee has $1.75 in dimes and nickels. the number of nickels is 11 more than the number of dimes. how many of each coin does he have?

What is the number 321,000,000 in scientific notation? also what is the number? ?

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)