Question 193055
Two equations for Kirk and Thor:
{{{d[k] = r[k]*t[k]}}}
{{{d[t] = r[t]*t[t]}}}
given:
{{{r[t] = r[k] + 25}}}
{{{t[k] = t[t]}}} (I'll call them both {{{t}}})
{{{d[t] = 279}}}
{{{d[k] = 204}}}
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{{{d[k] = r[k]*t[k]}}}
(1) {{{204 = (r[t] - 25)*t}}}
{{{d[t] = r[t]*t[t]}}}
(2) {{{279 = r[t]*t}}} 
From (1):
(1) {{{r[t]*t - 25t - 204 = 0}}}
From (2):
(2) {{{r[t]*t - 279 = 0}}}
Subtract (1) from (2):
{{{25t - 75 = 0}}}
{{{25t = 75}}}
{{{t = 3}}} hrs
Plug this result into (2)
2) {{{279 = r[t]*t}}}
{{{279 = r[t]*3}}}
{{{r[t] = 93}}}
Thor's average speed is 93 km/hr
check answer:
(1) {{{204 = (r[t] - 25)*t}}}
{{{204 = (93 - 25)*3}}}
{{{204 = 68*3}}}
{{{204 = 204}}}
OK