<span>2x+14y=-108
</span><span>63x+14y= 14 (multiply the second equation by 7 and subtract)
_____________
-61x=-122
x=-122/-61
x=2
2(2)+14y=-108
4+14y=-108
14y=-112
y=-112/14
y=-8
</span>
<h3>Answer: </h3>
about 1.768 seconds
<h3>Explanation:</h3>
Since the phone is <em>dropped</em>, the first equation applies. The final height is assumed to be zero, so we have ...
... h(t) = 0 = -16t² +50
... 16t² = 50 . . . . . . . . add 16t²
... t² = 50/16 . . . . . . . . divide by 16
... t = √3.125 . . . . . . . take the square root
... t ≈ 1.768 . . . . . . . . round to milliseconds
In this type of calculations, we decompose 13 by checking the lowest powers of the base, that is 40. for example we check 40^2, or 40^3 and compare it to 85
Notice
40*40*40=64,000
so we check how many time does 85 fit into 64,000:
64,000/85=752.94
85*753=64,005; 64000-64,005=-5
this means that

thus

Answer: 10 (mod85)
Remark, the set of all solutions is:
{......-75, 10, 95, .....}, that is 85k +10