When solving the following system of equations by substitution what would be a correct first step?

{x=y- 7 3x + 15y =- 1

A. 3x + 15 (y - 7) = - 1
B. 3(y – 7) + 15y = - 1
C. 3x + 15y (y - 7) = -1
D. 3x(y – 7) + 15y = -1

es una operación aritmética.

step-by-step explanation:

no se que fórmula requiera, pero te puedo decir que es adición. deberías revisar porque tema vas y ver que fórmulas puedes aplicar.

3

step-by-step explanation:

in standard form:

a= dictionaries

b= maps

you have to buy 3 dictionaries, so put a 3 next to the a (dictionaries) so that you can multiply them by each other.

a3+b= 60 (the amount of money you have)

we already know the cost of a=15 so replace a with $15

($15 x 3)+b=60

multiply 15 and 3 to get $45 and replace it with $45

45+b=60

and then replace b with 15 to get the total:

45+15=60

that means you have $15 left after buying 3 dictionaries.

15 divided by the cost of a map ($5) equals 3.

so you can buy 3 maps.

sorry if it was confusing!