Ok, so according to BODMAS (which stands for brackets, orders, division, multiplication, addition and subtraction), we have to solve the expression inside the bracket first, then solve the division and multiplication. So in this case we have,
3x times (7 times x)
= 3x times (7x) --> we have multiplied 7 and x)
= 21x^2 (^2 means squared)
Hope this helps!
