add c to b, subtract d from the result, then double what you have
Add c to b:
b + c
Subtract d from the result:
b + c - d
Double what you have means multiply the entire expression by 2:
2(b + c - d)
Add c to b:
b + c
Subtract d from the result:
b + c - d
Double what you have means multiply the entire expression by 2:
2(b + c - d)