The variables x +y are directly proportional, and y=2 when x=3. what is the value of y when x=9?

When the two variables is directly proportional to each other, they increase or decrease depends on how much it would be. In your equation x+y where two variables is directly proportional to each other, The increase of X is drastically 2 times greater from its last value. so it means that the value of Y should be 2 times greater than its value. So the value of Y should be 2^3 or 8.

1800×6.5%×30=b
b-1800=a

a) $1,710

b) $3,510