Answer: [tex]70a+21b[/tex]
Step-by-step explanation:
By definition, equivalent expressions have the same value but they look different.
In order to solve this exercise you need to remember:
1) The multiplication of signs:
[tex](+)(+)=+\\(-)(-)=+\\(-)(+)=-\\(+)(-)=-[/tex]
2) According to the Distributive property:
[tex]a(b+c)=ab+ac\\\\a(b-c)=ab-ac[/tex]
In this case you have this expresion:
[tex]7(10a+3b)[/tex]
Then, in order to find an equivalent expression to [tex]7(10a+3b)[/tex] you need to simplify it applying the Distributive property (Remember that you must multiply each term inside the parentheses by 7)
Therefore, through this procedure you get the following equivalent  expression that shows the sum of exactly two terms:
[tex]7(10a+3b)=(7)(10a)+(7)(3b)=70a+21b[/tex]
