Bernadette inherited 15000 and invested it in two municipal bonds , witch pay 7% and 9% simple interest. the annual interest is 1230. find the amount at each rate.

Let's say she invested "a" amount at 7% and "b" amount at 9%

we know, whatever "a" and "b" are, they add up to 15000, thus

a + b = 15000

how much is 7% of a?  well, (7/100) * a, or 0.07a
how much is 9% of b?  well, (9/100) * b, or 0.09b

we know the sum of the interest for both is 1230, thus

0.07a + 0.09b = 1230

thus  

solve for "a", to see how much was invested at 7%

what about "b"?   well, b = 15000 - a

1.17+3.99a. you combine the terms with a to create 3.99 and the 1.17 stays because it has no like terms or a variable

$18.25 ($365 divided by 20)