Question

13×(2a+c)+8×(2a-c)=========

Answer 1

$displaystylemathtt{13(2a+c)+8(2a-c) =26a+13c+16a-8c=}}\ \ =(26a+16a)+(13c-displaystylemathtt{8c)=}boldsymbol{42a+5c;} \ \ \ displaystylemathtt{OTBET: 42a+5c}$