A company finds that there is a linear relationship between the amount of money that it spends on advertising and the number of units it sells. If it spends no money on advertising it sells $400$ units. For each additional $$1500$ spent, an additional $15$ units are sold.

a$)$ If $x$ is the amount of money that the company spends on advertising, find a formula for $y,$ the number of units sold as a function of $x.($do not use commas in your formula$).$

$y=$

b$)$ How many units does the firm sell if it spends $$25,000$ on advertising? $($do not include any commas in your answer$)$ units

c$)$ How many units does the firm sell if it spends $$50,000$ on advertising? $($do not include any commas in your answer$)$ units

d$)$ How much advertising money must be spent to sell $700$ units? $($do not include any commas in your answer$)$

$

e$)$ Which of the following statements CORRECTLY explains the meaning of the slope? $($select all as there may be more than one correct statment$)$

A$.$ If the company spends an additional $$1000$ on advertising, it will increases the number of units it sells by $10.$

B$.$ If the company spends an additional $$0\mathrm{.}01$ on advertising, it will sell one more additional unit.

C$.$ In order to sell one more unit, the company would need to increase the amount it spends on advertising by $$100.$

D$.$ If the company increases the amount of money it spends on advertising by $$400,$ it will double the number of units it sells.

E$.$ None of the above