The sum of 5x and 2x is at least 70

Sum means add

5x+2x is at least 70

is at least means >

so it is

5x+2x>70

(5x+2x can be combined to get 7x and 7x>70 divide 7 get x>10)

Set up an equality.

"sum," "and" means to add, and "at least" means greater than or equal to.

5x + 2x ≥ 70

7x ≥ 70

x ≥10

Remember in inequalities you solve them almost like normal equations (you can add, and subtract the same) BUT if you multiply by a negative you must flip the sign. You don't have to flip the sign in this case because there are no negatives.