Lets call 'C' the cost to rent the kayak,
C = $25/day ($25 per day)
lets call 'D' the number of days the person would like to rent the kayak,
D = 5 days
Lets call T the total cost to rent the kayak
T = ??
To come up with the equation we can think of other scenarios. If it costs $25 per day, how much would it cost to rent for one day?
$25
How much for two days?
$25 + $25 = $50
lets factor this...
$25(1+1) = $50
$25*(2) = $50
Three days?
$25 + $25 + $25 = $75
lets factor this...
$25*(1+1+1) = $75
$25*(3) = $75
Four days?
$25 + $25 + $25 + $25= $100
lets factor this...
$25*(1+1+1+1) = $100
$25*(4) = $100
so in general we can see the equation should be,
Cost*days = total cost
or
C*D = T
so for our question where
C = $25/day
D = 5 days
we have
($25/day)*5days = $125
T = $125