You can write the relation between distance and time, as follow:
y = kx
where y is the distance, x is the time and k is the constant of proportionality.
k can be obtained with the given information, as follow:
k = 90/30 = 3
Then, the equation of the relationship is:
y = 3x,
for a time of 10 seconds, the distance traveled is:
y = 3(10) = 30
Hence, the answer is:
y = 3x , 30 feet