The formula for the number of seats in a row is f(x) = 5x + 5 in which x is the row number. And the amount of seats in the 10th row would be 55.
You can find this by using data points (1, 10) and (2, 15). Then we can solve for the equation by first finding slope (m). The slope formula is below.
m = (y1 - y2)/(x1 - x2)
m = (15 - 10)/(2 - 1)
m = 5/1
m = 5
Now that we have that, we can find the intercept by using slope intercept form and a point. We'll continue to use (1, 10).
y = mx + b
10 = 5(1) + b
10 = 5 + b
5 = b
This gives us the equation of f(x) = 5x + 5. Now we can us the 10th row for x and see how many seats there will be.
f(x) = 5x + 5
f(10) = 5(10) + 5
f(10) = 50 + 5
f(10) = 55