These are easy if you know " FOIL ". That's a procedure that takes you through multiplying two binomials.
FOIL stands for
-- <u><em>F</em></u>irst terms
<span>-- </span><u><em>O</em></u>utside terms
<span>--<em> </em></span><u><em>I</em></u>nside terms
<span>--<em> </em><u><em>L</em></u></span>ast terms
and that's how you keep everything straight while you're doing it.
(ax + b) x (cx + d)
Multiply First terms . . . 'ax' times 'cx' = <em>acx²</em>
Multiply Outside terms . . . 'ax' times 'd' = <em>adx</em>
Multiply Inside terms . . . 'b' times 'cx' = <em>bcx</em>
Multiply Last terms . . . 'b' times 'd' = <em>bd</em>
Now addummup:
(ax + b) x (cx + d) = <em>acx² + adx + bcx + bd</em>
From there, you can look for opportunities to make it look cleaner and prettier ... factoring, combining like terms, etc.
Since the head of the trail is located at (3, 0), the trail moves 3 units north with each move and the map extends to 40 units to the north, then the number of 3 units in 40 units is 13.
Thus, he can move only thirteen 3 units to the north and hence, thirteen 1 unit to the east.
Thus, the x-coordinate of the foot of the trail is 3 + 13 = 16 and the y-coordinate of the foot of the trail is 0 + 3(13) = 39.
Therefore, the location of the foot of the trail is at (16, 39).
3 * 7 = 21, so

Then

and you can rationalize the denominator to write this as

Giving You Up by Kameron Marlow. Love that song