Evaluate each integral below. What is the difference between them?

1. What is $\int _ { 0 } ^ { x } ( 2 t + 5 ) d t$?

   First Step (a):

   $\int _ { 0 } ^ { x } ( 2 t + 5 ) d t = t ^ { 2 } + 5 t | _ { 0 } ^ { x } =$

2. What is $\int _ { 4 } ^ { 9 } ( 2 x + 5 ) d x$?

   First Step (b):

   $\int _ { 4 } ^ { 9 } ( 2 x + 5 ) d x = x ^ { 2 } + 5 x | _ { 4 } ^ { 9 } =$