Demogorgon

Parallel lines have the same slope.

So that,

for Ax + By = C, we have y = (-A/B)x + C/B, where the slope is -A/B

for Ax + By = D, we have y = (-A/B)x + D/B, where the slope is -A/B

Hence, the two lines are parallel.

Note that:

if A = B = 0, y = 0/0 + C/0 (or D/0). The lines are undefined.

if C = D, it is a single line crossing the ordinate axis at the same point.

T(t) = T_A + (T_H - T_A)e^-kt

where,

T(t) = Temperature at time t,
T_A = Ambient temperature (temp of surrounding)
T_H = Initial temperature of the cake
k = constant of proportionality (negative because of cooling)
t = time.

Now, for A, we have,

120 = 70 + (180 - 70)e^-kt, or $$\frac{}{}$$e^-kt = 5/11

For B, i.e. to find t, you need k.