The is used for an event that continues to occur at the present moment in time. simple present present perfect present progressive present perfect progressive

It's C.

"present progressive"

Hello! C. But let me explain to you the differences: Present Simple for the future, when it comes to events that occur regularly, on a schedule. Present Progressive is used for what is happening "at the moment", even if this moment is stretched in time. Present Perfect When the event occurred at an uncertain time in the past. Present Perfect Progressive this time expresses a prolonged action, which began to occur in the past and is still in progress or has just ended.

substitute y = 2x - 4 to x + 2y = 12:

x + 2(2x - 4) = 12     use distributive property

x + (2)(2x) + () = 12

x + 4x - 8 = 12     add 8 to both sides

5x = 20     divide both sides by 5

x = 4

put the value of x to the first equation:

y = 2(4) - 4

y = 8 - 4

y = 4

im not