1.
When you have the length of two sides and the angle between them, the triangle is totally determined. This is, there is only one segment that can complete the triangle: its length and position is totally fixed.
The way I like to solve proportions is by cross multiplying and dividing. First yo multiply the diagonals and then you divide by the other number. So if your proportion is 7/5 = x/3, your equation would be 7*3/5. So 7*3 is 21, so your equation is now 21/5. With some long division, you'll see that 21/5 = 4.2 That's your answer, feel free to ask more questions if you need!!(:
A = amount invested at 4%.
b = amount invested at 9%.
we know the total amount invested was $26500, thus
a + b = 26500.
whatever% of anything is just (whatever/100) * anything.
how much is 4% of a? well, is just (4/100) * a, or
0.04a.
how much is 9% of b? well, is just (9/100) * b, or
0.09b.
we know the interest yielded for both amounts adds up to $1510, thus
0.04a + 0.09b = 1510.

how much was invested at 9%? well, b = 26500 - a.