Linear Equations

Solve.
$$\dfrac{5z}{20}=10$$
Solve: $$\displaystyle \frac{34}{3x+4y}+\displaystyle \frac{15}{3x-2y}= 5$$ and $$\displaystyle \frac{25}{3x-2y}-\displaystyle \frac{8.50}{3x+4y}= 4.5$$
A two-digit number is $$3$$ more than $$4$$ times the sum of the digits. If $$18$$ is added to the number, the digits are reversed. Find the number.
Simplify
$$\dfrac { 2x+7 }{ 5 } -\dfrac { 3x-11 }{ 2 } =\dfrac { 2x+8 }{ 3 } -5$$
$$A$$ and $$B$$ each have a certain number of mangoes. $$A$$ says to $$B$$, "if you give $$30$$ of your mangoes, I will have twice as many as left with you." $$B$$ replies, "if you give me $$10$$, I will have thrice as many as left with you," How many mangoes does each have?